One should note that while it is true that the last CLISP release was a long time ago and there is not a lot of development going on right now, it's not dead. Bruno Haible just commited last week.
I caution anyone reading this to not take this summary at face value. If you're interested, you should read the linked threads for yourself. I'd say you can leave out that someone followed up on some technical detail three years later, but you be the judge.
FWIW, my takeaway was the exact opposite. How the original async authors were treated was a disgrace. It showed, to me, that there were deep problems with the vim dev community. Forking off neovim was the best thing that could happen. I'm so glad someone had the energy to do so.
That said, I'm super grateful for Brams work on vim. It was my tool of choice for many years.
The repository is now at https://gitlab.com/gnu-clisp/clisp