Not sure if that will be possible after the move to CS2. You would think so, but at the very least, "Kisak-Strike: Gentoo Offensive" will exist.
idtech still towers over the source engine for any real "small" projects. The community support + license + codebase is just so much better.
The only reason to use source is if you are a superfan who wants to make derivative stinky cut-content projects, and VR ports. Otherwise, you're just enslaving yourself to the valve megacorp(unless you can afford an apex-style deal).
idtech... 4 ? How badly do you hate your job that you agree to put up with this piece of shit ? Even pulling out Godot would be less crappy and have more support than an engine targeting DX9 and OpenGL released in 2002. idtech 4 is barely better than _goldsrc_. Some things ought to die, and idtech 4 is better suited to a museum than any real game these days. The lack of any useful and modern tools should already be a screaming red flag.
You could dev a PC AAA game and released it only for elf/linux. It is so easy to install free mainstream elf/linux distros, ppl will probably do it to play that big PC AAA game.