Having been sent back to the Rift to deal with the problematic Reachmen who are allied with the Worm Cult, I make a detour to Riften (one of many to unload gear) and while there complete both Mages and Fighter's guild quest lines. For the Mages one, Shalidor uses the tomes to transport us to his missing island of Eyevea which Sheogorath has left littered with dremora. After cleaning those up we get to keep the island though Sheogorath does take the now insane tome decypherer, Valaste, with him back to the Shivering Isles. Shalidor still rewards me with a "library" type function (recall all books / papers through a menu).
Afterwards, I went to track down the murderous Argonian fighters guild master with the Fighters Guild to Coldharbour, where she openly admits to the murder of the previous leader - all because Meridia demanded to get the Fighter's Guild involved against Molag Bal. Conveniently, his "back up" weapon is here and I end up assisting her in destroying it along with a traitorous khajiit who Molag Bal transforms into a Demon Dragon thing.
Molag Bal should hand out boons more often - that looks cool!
The murderous Argonian is spared, but stripped of the guild master title which goes to Mr. replacement guy. I'm just happy that's all done and I can go back to exploring!