Zechariah 14:16 And it shall come to pass, that every one that is left of all the nations which came against Jerusalem shall even go up from year to year to worship the King, the LORD of hosts, and to keep the feast of tabernacles.
17 And it shall be, that whoso will not come up of all the families of the earth unto Jerusalem to worship the King, the LORD of hosts, even upon them shall be no rain.
18 And if the family of Egypt go not up, and come not, that have no rain; there shall be the plague, wherewith the LORD will smite the heathen that come not up to keep the feast of tabernacles.
19 This shall be the punishment of Egypt, and the punishment of all nations that come not up to keep the feast of tabernacles.
Not only do we need to determine what this is meaning, we also need to determine when it is meaning. The latter being mainly the focus of the OP.
When it comes to prophetic events in general, how can one reasonably argue that chronology is irrelevant? For example, in Zechariah 14 would anyone suggest that verse 12 is fulfilled prior to verse 2? Probably not, right? And why is that? Is it not because chronology is obviously relevant after all, otherwise why would it matter when verse 12 is meaning in relation to when verse 2 is meaning?
Many insist that nothing in Zechariah 14 involves any events outside of this present age, and for certain, verses 16-19 don't. But is that what the chronology of events show to be the case?
IMO, some of Zechariah 14 pertains to this age and some of it pertains to an age post the 2nd coming. Therefore I place what is recorded in Zechariah 14 into 2 categories.
The first category, I will label it A), events pertaining to this age.
The second category, I will label it B), events pertaining to an age post the 2nd coming.
The verses I see pertaining to A) would be all of the following---1-5, 12-15.
The verses I see pertaining to B) would be all of the following---6-11, 16-21.
But let's assume that it is incorrect for me to assume that verses 16-19 fit category B), that they instead fit category A). In order to conclude they fit A) rather than B), a cpl of things have to be factored in first, though. For instance, verse 12. Is not verses 16-19 meaning after the fulfillment of verse 12, the fact these remaining obviously didn't encounter the same fate at the time, that those meant in verse 12 did? Because if they did, how does one explain that the text in verse 16 says this---that every one that is left of all the nations which came against Jerusalem shall even go up from year to year to worship the King? Those that received the punishment described in verse 12, are or are not these of the ones of all the nations which came against Jerusalem? Doesn't this simply mean that not everyone living in the nations that attacked Jerusalem were even involved in the attack? They simply lived in the nations involved in the attack, and not that they were also participants of the attack, thus why some are spared and some are not.
The next thing to factor in, has verse 12 even been fulfilled yet? Can anyone convincingly argue that it has already been fulfilled? I don't see how.
Since the OP is getting rather lengthy already, I would like to focus on one more thing involving the verses in question, meaning this---that whoso will not come up of all the families of the earth unto Jerusalem to worship the King, the LORD of hosts, even upon them shall be no rain. How does one apply something like that to this age, in any sense? When is the last time one has ever heard of any families residing on the earth the past 2000 years, that have been threatened with no rain for refusing to come up? Since no reasonable person should disagree that Zechariah 14 involves events pertaining to the last days if that same person agrees that the last days began 2000 years ago with the first coming and that we are still in the last days even today, how then can anyone reasonably apply what is recorded in verses 16-19 to that of the past 2000 years?