The AC Stark effect (and I believe the DC also) is species dependent and spin dependent. It cannot be the cause of the cosmological redshift which is observed to be species independent. We measure the same relative amounts of redshift across the sky regardless of the special composition of the star or object in question or the intervening space.
It really annoys me when astronomers use terms like "cannot" with nothing more than a handwave argument.

Plasma redshift (whatever the actual 'cause') absolutely can cause redshift, and it is capable of explaining all the observations typically associated with expansion/acceleration models. All that would be required is an *electric* universe, and that seems to be the one thing that astronomers *refuse* to consider.
You still 'appear' to be confusing individual interactions between individual photons and individual plasma particles with the *overall* effect of many such interactions over distance and time.
Incidentally, I don't think the electron density presented in the Chen paper (1018 cm−3) reflects the electron density in the intergalactic plasma at all, so I'm at a complete loss to think how you would generate consistent cosmological redshift from the Stark effect applied in this manner.
FYI, their "proposed mechanism" (Stark effect), is not necessarily the actual 'cause' of that plasma redshift observation. I'll grant them the benefit of the doubt for the time being, but it's not a given.
You seem to downplaying the significance of the effect of traveling a great distance, and the fact it makes up for a localized concentration of current. More importantly, in any plasma cosmology theory, there is a concentration of current in and around all galaxies and objects in that galaxy.
By the way, if a concentration of current is what you're looking for in terms of supporting these redshift concepts, solar flares are an *excellent* place to start looking for such support, and FYI it's already been done.
http://vixra.org/pdf/1105.0018v1.pdf
Excellent paper IMO. I'm still trying to digest the significance of his findings in relationship to Iron and Silicon. Those two particular elements are in fact located at the lowest layers of the atmosphere in the solar model on my website. In a very real way, he's right about that point IMO. I'm still trying to figure out what it all means, but I'm absolutely certain he's on to something. That simply cannot be a coincidence IMO.
The Stark effects would and should be tiny compared to the observed cosmological redshift for objects with a high value for z,
Where did you come up with the the "tiny" effect? I assume that you're assuming that the universe does not experience much current flow based on that accusation/handwave of an argument. You can't make that assertion without knowing something about the number of free electrons between here and there.
not to mention the fact that Stark effects aren't that simple (consider the various types for starters - DC, AC etc.),
They aren't simple, but they do yield some really fabulous results in terms of the data they can produce. Ashmore's findings related to Iron and Silicon emissions originating in a different layer of the atmosphere was really insightful IMO. That kind of information is dynamite, particular when we also consider the fact that convection rates are only about 1 percent of mainstream predictions. Both observations suggest a process of 'mass separation" in the solar atmosphere is highly likely. That simply blows my mind quite frankly.
so proposing that they could be the cause of the observed large cosmological redshift from a very small effect observed in carbon nanotubes is untenable.
It's more of a net (total) effect of light passing through *all* the elements in spacetime combined, and averaged over distance. The overall effect is a broadened signal that will tend to disperse some percentage of the light and will tend to "heat" the material of spacetime. Somewhere in one of these threads I posted a link a paper that discovered that galaxies are at least twice as bright as we first believed. This in fact directly related to the scattering effects that take place. Chen just happened to use carbon, but the process is likely to apply to all elements.
(In the Chen paper, the excess electrons in proximity to the carbon nuclei would still exhibit a Coulomb force to the atomic nucleus, don't they? Not the interaction you'd be seeing out there in the intergalactic plasma...)
You're going to need to take the NET effect of light passing through MANY elements, not just carbon, not just hydrogen, not just helium, not just neon. It's a cumulative effect that involves several different interactions IMO.
You're still not over the blurring problem. I haven't calculated what I think the blurring should be...have no tired light proponents done this?
Yes, in a round about way, although not directly related to 'blurring' as you put it. HH's C# code does seem to include scattering effects that require minimal light sources to travel vast distances. In terms of "blurring" rather than simply photon loss, I haven't seen anything trying to focus specifically on such an issue so far, but keep in mind I just found out that plasma redshift had been confirmed in the lab a few weeks ago, and I've only been through a tiny fraction of the published literature that exists on various redshift models.
Even if we take Compton scattering, the direction of the emitted photon depends entirely on the energy level, where x-rays would be more prone to an isotropic scattering than visible light - which would tend to scatter forwards, in the direction of original travel, to be fair. It is possible to work out the angle of scatter depending on the respective energy levels involved.
IMO the whole blurring argument is a handwave of an argument, particularly in light of recent discoveries, like the fact that the universe shines twice as brightly as we once believed. These are actually 'bombshells" in terms of what we really know about the universe. Granted, I would expect a certain amount of blurring to occur, but I would expect that most scattering events would deflect the photon so far away from the Earth that we'd simply never see it. The only "blurring" we'd be likely to observe would be related to scattering events inside our own galaxy and most likely inside our own solar system. Most of the rest of the deflections are likely to simply make the photon travel somewhere beyond our line of sight IMO.
To obtain the reasonably defined images we have of distant galaxies, (not even the colossally distant ones), the photons emitted have to be traveling in reasonably the right direction - logic alone dictates that.
Sure. We have to assume that those particular photons (that arrived at Earth) are likely to be the photons that were the "least" scattered photons of all the photons that came from that distant object. Logic would tend to dictate that those particular photons are unique in that way.
If the image is equally sharp across the various frequency bands, irrespective of time of arrival (which is affected by dispersion, for starters, so the notion that we expect all the light to arrive 'at once' is a little silly) then the photons need to be emitted in the correct direction or with minimal scatter at all energy levels.
Again, every photon of every wavelength we observe happens to be a "lucky photon" that experienced a minimum amount of deflection during it's travels. It doesn't matter which wavelength we consider, they are all "lucky" photons in the sense that they experience the least amount of scattering deflection.
I don't buy that this is possible with the Stark effect. It is possible with Compton scattering in certain frequency bands, but not others (particularly the higher energy levels).
Keep in mind that I'm not emotionally attached to the Stark effect, NTL models, or any other 'single' explanation for that matter. It could be, and probably is a "net effect" caused by a lot of types of interactions in plasma, including Thomson scattering, Compton scattering, NTL interactions (?), Stark effects, and who knows what else! I simply don't know for sure until and unless I investigate further, both in the cosmological data, and in the laboratory data. What is clear however is that it's a very "real' and measurable process.
Whereas - inflationary theory doesn't require any interactions which means that we see nice, clear images of distant galaxies.
Yes, yes, we know how your mythological sky entities work and how they are invisible to all forms of light.

The problem however is that they really aren't all that "clear" at the highest redshifts, and the light apparently doesn't all arrive at the same time.
I'll deal with your propagation issues later, but you should remember that the universe is not a perfect vacuum...I notice in the preprint of that particular paper they didn't bother to ascribe any 'new physics' to the observations, and they don't seem to have done much follow-up.
I'll need to see you deal with this issue before I"m convinced that you're considering all the data, and not just cherry picking the data you like.