Nothing hypothetical about it. It is an exact solution to Einstein's equation, the one you say you accept.
It's absolutely a "hypothetical" universe that is devoid of any *source/cause* of geometric curvature, gravity, or spacetime. It's certainly a hypothetical construct since you cannot demonstrate your claim in controlled experimentation.
Too bad they don't. Otherwise galaxies would be unstable.
It's a good thing that gravity still plays the larger role in the push-pull process of galaxy formation. Then again there's all that million degree plasma around the galaxy and of course all the current that sustains that plasma at millions of degrees. Put the whole ball of wax together correctly, and I'm sure it works out just fine. Peratt did a whole series of computer simulations related to galaxy mass layouts based mostly on pure plasma physics.
Fine, put matter in there. Like Einstein did. What do you get? Expanding space.
Nah. In Einstein's case he got expanding or contracting spacetime when he abandoned his blunder theory, whereas in your case you've got supernatural claims galore stuffed into a blunder theory that remain unsupported in the lab and will *always* remain unsupported in the lab.
What do they use as the stress-energy tensor? What do they use as the equation of state? Show me the solution to the GR equations.
I have *no clue* what you *actually* intend to use to do anything. You've literally got *nothing*, so the logic of applying GR to "nothing" is a lot like attempting to apply MHD theory to "nothing". It's not applicable in the first place.
You keep *insisting* on trying to disconnect the *cause* (mass/energy concentration) from the *effect* of those equations (curvature/motion/stress-energy tensors) that you're trying to use. That's not even logical to start with.
I'm sure you've created an entire mythological brand of blunder theory that works on paper, but the problem is that it doesn't work in real life. In the real universe we live in, your theory *left out* the EM fields, the inelastic scattering and the signal broadening that is observed in laboratory plasmas. As a result, you're forced to attempt to make up for it with supernatural constructs galore. You've got four unsupported claims going so far:
Space expands
Inflation causes space to expand
Dark energy causes space to accelerate
Exotic matter makes up most of the universe
Not one of these four "acts of faith" on the part of the believer enjoys any empirical laboratory support. All four unsupported allegations only occur in *one* (and only one) otherwise *falsified* cosmology theory that we know for a fact left out EM fields and scattering processes in plasma.
Sorry, but even compared to my "faith in God", your *unwavering faith* in your four supernatural claims is in a completely different category. Even I have some hope of empirical vindication in the lab, in real controlled experimentation, if not now, perhaps sometime in the future.
You can't even *hope* for laboratory vindication of any of your claims. Talk about pure acts of faith in supernatural constructs. Lambda-CDM requires more supernatural constructs, and more acts of faith in the unseen (in the lab) than an average religion.
I don't think you and I are ever going to see eye to eye on your expanding space claim unless you can demonstrate your claim in a lab, in controlled experimentation. If you cannot do that, I have several *other* options to choose from, including gravitational redshift (time dilation around heavy objects), moving objects and inelastic scattering. I have no need for your supernatural constructs because I have no desire to leave out important characteristics of plasma and the observations of light traversing various plasmas. As long as you insist on leaving out the EM field and scattering aspects of plasma, of *course* you'll continue to wallow around in the literal "dark ages" of astronomy.
At the rate the mainstream is going, Birkeland was already more than 100 years ahead of the mainstream at understanding basic plasma physics in current carrying plasmas, and maybe 200 years.

It took the mainstream 60 years to figure out Birkeland was right about aurora, and I suspect it will be over 120 years before they figure out he was right about suns acting as cathodes with respect to spacetime. I have no confidence at all that the mainstream understands anything correctly (not pseudoscience) about plasma physics, solar physics or astronomy in general. Lambda-CDM is 95 percent *supernatural construct* and only 5 percent token physics as window dressing.
Sorry, but IMO empirical physics always *eventually* trumps supernatural constructs. Sooner or later EU/PC theory is going to replace that supernatural dark sky nonsense with real physics. It's only a matter of time.
FYI, now that BBSO has been seriously upgraded, and IRIS images are starting to flow, how long can the mainstream keep pretending that the flux ropes aren't already radiating at high temperatures *before* they exit the photosphere? Another year? Two? Five? Ten?
Sooner or later the spaceweather folks are going to catch on the electrical nature of the solar atmosphere, and the jig will be up for solar physics and what Alfven called "pseudoscience". It's really just a matter of *when*, not if.