I have a few extensions, notably an update to subtle-brackets, which I cross-published. It's relatively painless - Eclipse running Open VSX is clunky, but no more clunky and UX-weird than the marketplace (which holy shit, talk about terrible UX). The issue is that VSCodium has holes, and not all extensions will run correctly.

I'd like to see a hard fork for VSCodium, where the community could make UX/DX upgrades that VSCode's Microsoft-employed gatekeepers have summarily shut down time and time again (see: issues on the find/replace dialogs)