Hey there,
I have practically zero experience with the Steam Workshop, but as Immersive Interiors ticks all the criteria for being able to be uploaded there, I thought that I'd give it a go in order to offer the mod to more people. I already have a BSA so when I click to upload to Steam from the CK it asks me if I'd like to use that one. Regardless of whether I choose yes or create my own, I then get stuck on this screen:
http://i.imgur.com/XP3XMUV.png
Which doesn't look anything like the screen detailed in the CK wiki:
http://www.creationkit.com/images/a/a5/SteamUploadDialog.jpg
Clicking OK doesn't actually do anything then. I know the whole "Getting details on published files..." thing is meant to be if you've already uploaded it, but I have not and there is no mod with the same name. This happens for any mod I try to upload.