It effectively already is. It may end up in the same domain as Haiku OS, Plant 9, or Squeak, but they are all still interesting domains of research.
Let's hope 9front is a seed, yet to fully germinate.
When was it anything else? The 80s? I've can count the number of Smalltalk jobs I've seen in my career on my hand (but I have seen them)
The opposite. With LLMs you can now pick up any one of these obscure language and write a full blown AAA game engine in them. Or a database. Or a web framework. Or... anything you set your mind to. The language no longer matters. btw LLMs are exceptionally good at Smalltalk/Haskell/Perl/FORTRAN and other old/uncommon languages.