I don't have all my tools avaliable so I have not researched this. But in theory, would setting up a shadow mesh together with an actor(actor looking like an interior mesh), give a usable result in terms of interior shadows?.
Alternatively, you could just make an actor/interior shadow mesh without the interior parts. One would have to be made for every interior piece in the game and then handplaced or matched with some generator to do it automatically.

I recon, somebody should try it out. I'm curious, maybe someone already did experiment with this.

Before moving on, it's imperative that you know that I know about OpenMW and Skywind. And I also know about the baked shadow map mod for (Vivec?) I think. While all those are phenomenal in their own way. I'm just thinking if we can push the workings of the engine in some interesting ways.

I also recall Hrnchamd did try to get interior shadows working through MGEXE, mayhaps in cojunction with MCP. I think the main issue had to do with the share number of lights being really high and a steep difficulty of implementing deffered lighting(lighting method that can process lots of lights quick and efficiently). Mind you new techniques may have popped up in recent years, this was all the buzz like 4-5 years ago. Deffered lighting that is.

This is an open thread to discuss ways to make this a reality. SSAO does a great job of giving us more depth perception, but it's time to take another step. Continue making Morrowind spectacular.

Any other ideas, comments, thoughts?