But the real question for anyone else in particular about any of this is "Does it actually matter?"
Now perhaps for someone like you or Mike Shea... designers who have to decide whether or not to hitch your future designs to the 5E24 wagon or not... trying to forecast 5E24's future is only doing your due diligence. That makes sense. But for the rest of the playerbase? Does it matter ultimately whether or not 5E24 lasts as long or does as well as 5E14 did? I don't know that it does. So it's more a discussion of curiosity rather than necessity.
I tend not to think much about where to hitch up my wagon. I write what I want to write for the systems I want to write for. I love 5e but I'm not in love with any one particular flavor so I've been writing for 5e. In City of Arches, I've included tables to help you find monsters across multiple 5e monster books. I didn't include subclass options. Backgrounds are lightweight and easy to modify. I have two monster stat blocks (which we're revising because I stupidly went with the "reaction" style legendaries and it doesn't look like anyone is sticking to that).
I want to write stuff for 5e regardless of the 5e people play.
I know other creators who spend a lot of time writing for specific brands of 5e – D&D 2024 or Tales of the Valiant – and they have specific things they want to write for that only those systems have. I'm much more interested in writing products that can be easily played not only with any 5e flavor but even other fantasy D20 games.
I actually don't have another big project in the works yet. I'm sort of seeing how things play out this year and focusing on small Patreon products for the short term while we get City of Arches out the door.