Thomas Liu
tyl089
Yeah, this is an untapped questline... It would have been great if you could partner up specifically with Mjoll to take down the Thieves Guild permanently. She seems so altruistic and actually cares about Riften, it's a shame that there wasn't any way you could help her aside from helping her recover her old sword, Grimsever.
Here's hoping Bethesda will do a DLC for that quest line... Clearing the Rift.