Usually programming languages need that killer project to sell themselves, instead of being something only language nerds play with, Bun was one of such projects.

Bun still exists. as does tigerbeetle

Lets see for how long, after the acquisition.

And if they did, what could they possibly do?

As Bun uses Zig quite a lot, I expect them to be quite active in the Zig forums and submitting patches and feature requests.

I was thinking of things like AI-generated patches submitted by Bun to the Zig project, or feature requests by Bun for AI-specific use cases... that could create a really bad atmosphere between Zig and Bun people if the Zig Foundation continuously rejects their contributions/requests/discussions.