I hope not, having a consistent ecosystem where all parts of the system share the same building blocks is one of the beautiful aspects of SerenityOS.

For example in this video Andreas implements palette support for commands (commands are usually shown in the menu bar or contextual menus) and it has the nice side effect of immediately enabling them on every GUI program, even the desktop itself!

https://www.youtube.com/watch?v=LAqGLkRCFb8

I think Zig can be a polite guest in SerenityOS thanks to Zig's general interest in supporting uncommon targets, but the hosts are C++ and Jakt.

I really like Jakt:

https://github.com/SerenityOS/jakt

judging by past answers given, no. this is just so you can develop on serenity using zig, but anything in-tree needs to be C++ (or Jakt once that's ready)

Jakt seems to at least be ready enough to write Nintendo emulators. :)

It's more about integration into the rest of the system. E.g. the jakt and serenity string classes differed, so now the old string class has been deprecated and replaced by the jakt one. I'm not actively involved in the project though so I couldn't tell you much more than that