Just how many 5E RPGs can there be?
Uncountably many. This is only partially a joke. Due to the almost totally hands-off, advice-empty nature of 5e, in theory every
session at every table can be a different 5e. Of course, in practice, these things are fuzzy clouds, not hard points; in which case, it's rather hard to answer, because the line between one "5e RPG" and another is vague at best and possibly indeterminable.
How many will the market and community support?
Depends on what you mean by "market," "community," and "support." I am not trying to be persnickety; there are multiple meanings of these words which change the answer.
Level Up, for example, seems to qualify as a "different 5e RPG,” and it is going strong enough to get new products like a boxed set. But some argue that it isn't actually different, for the same reason (say) Bo9S or Essentials were not different from 3e or 4e.
Critical Role AIUI has moved toward using its own system. Other RPGs piggybacking on 5e, do those count as "another 5e RPG"? Or are they wholly distinct products?
Does the "market" include video games like Baldur's Gate 3? If so, then that already opens the door to more variations because we already have two, Solasta and BG3, which both intentionally diverge from current 5e in specific ways.
"The community" is a heterogeneous thing. It does not have monolithic preferences or patterns (one of several reasons why I find certain things about 5e development frustrating.) Depending on which segments we emphasize, different interests come to the fore.
And what counts as "support"? Staying in print? Some would call that full support, others could just as easily say that a lack of new products means it's dying or even dead (a common refrain when speaking of 4e.) Getting new flavor products but few to no new rules elements? Some would call that wonderful, support without bloat, while others would decry it as allowing it to stagnate and leaving players stuck with the same paucity of options forever.
Personally, I'm of the opinion that not only CAN 5e support more variants, it
should do so. As much as possible, build up a common language, and then use
horizontal segmentation. 5e has, somehow, managed to skate by on pretending to be all things to all people. I don't think that is a stable state of affairs.
So, how many different versions of 5E can the community support?
Purely IMO (as all these answers are): Several. More than four.
Will the presence of unofficial 5E games cause disruptions for WotC with the 2024 roll out?
What is a "disruption"? E.g. if you mean "will these variants result in less than 100% adoption of 5.5e?" Then the answer is yes, absolutely. If you mean "will it prevent 5.5e from being financially successful?" Then the answer is almost surely not.
Are any non 2024 5E games even viable once it rolls out?
Yes. If they're viable now, adding 5.5e won't change that. Frankly, if someone already bought something third-party, they're far too committed for a new official release to change their minds that much.
Will people continue to play 2014 5E?
Some, yes. Just as some continued to play 3.0. Most will jump ship though, unless it proves spectacularly unpopular, which seems unlikely at this point.