Will this mean the end to NeoVim, whose main (one of) selling point is the tree-sitter out of the box? I hope not, as I am the long time user and supporter of the project.
Very strange attitude towards open source. One guy decides to stop working for free, leaving all of his work publicly accessible for anyone to continue to build upon, and the response is "well, I guess that's the end of that project".
I'm guessing the attitude of "users and supporters" of the project such as shushtain complaining and wanting clason to do all the work instead of just doing it themselves, was a factor in him deciding to step away from the project.
tree-sitter still works. Many features are implemented in neovim itself. This project provides an easy way to set up parsers for various languages (including installation and retrieval of necessary queries), along with some quality-of-life features. You can just fork it, and it will work perfectly fine for the 0.12 cycle (barring any underlying parser changes), or you can fork the previous version on the master branch if you want to keep using 0.11.
Considering this is a very common plugin in the neovim ecosystem, it will probably get forked and maintained by someone else, like null-ls was forked into none-ls.
I'm guessing the attitude of "users and supporters" of the project such as shushtain complaining and wanting clason to do all the work instead of just doing it themselves, was a factor in him deciding to step away from the project.