So out of all the official plugins, Siege at Firemoth is the only one I really play with, but it seems really lazy in it's writing. Firemoth is an archipelago seemingly created by one of Red Mountain's past eruptions, and is in a highly strategic location. It's also an extremely plentiful ebony mine. It makes no sense to me that after the player cleared it out, the Empire would just forget about it, being of the importance that it is. That being said, I'd really like a mod that adds a questline to rebuild the fort. The fort itself could provide services like any other legion fort, and there could perhaps be more involved, but the main thing I want is a questline similar to the Raven Rock questline that involves the player helping to rebuild and re-garrison the fort. I'm aware there are mods that convert the fort into a player home, but those aren't what I'm looking for. That being said, if I get more experienced with questing, I may eventually make this myself, but for now I'd just like to put the idea out there, if it hasn't been suggested already.

This reminds me that years ago, when I was active in the French modding community, I was working on something like that.

The Fort had been extended a bit with a lighthouse, and the horde of undead got some added variety (crossbow skeletons guarding the fort, etc.) and a script so that they'd all die after Grurn was slain. The Khajiit Legion soldier you can free would be your go-to NPC for all rebuilding and restaffing of the Fort; and the three mercenaries were to become a full-fledged set of companions with Grumpyscripting and additional quests for each. The boat was turned into a big one (with an interior cell) so that it could also serve as a mobile headquarter with various destinations.

Obviously, I lost interest partway through. Problem of being far too ambitious.

There's the Ward of Akavir that expands the quest version of Firemoth, but doesn't rebuild the fort. There's a few Firemoth expanded mods, but they all basically make a home rather than an imperial fort.