For the mods at least, the dev interview at PAX clearly had a moment when one guy said "the possibilities of combination with civilizations switching is going to be higher, especially with the modding community adding custom civs.

But since they said a huge part of the playerbase is console, I'm guessing mods won't be using the steam workshop but the launcher so that consoles can have mods...

As for Linux support yeah I would like to hope, maybe the stats of Civ6 on the steamdeck could push them to make it compatible but if they have denuvo I doubt it...