The author wrote WebKit’s allocator and worked on JavaScriptCore for over a decade. I really enjoyed his posts on the WebKit blog over the years like this one on the concurrent garbage collector (2017) https://webkit.org/blog/7122/introducing-riptide-webkits-ret...

I don’t think so much is fil-c itself, but from the looks of the diff it’s a new platform essentially. That can require porting existing software generally which you can read from the posted diff