some either stand alone IO's and or IO sets related to the various factions organisations and super villains/heroes would add a fair amount of fluff/character and also fill the grinding out a set niche that people seem to be fond of these days also pvp IO sets again linked to various in game organisations/powerful individuals just farmed from pvp participation
also tie as many of the regular IO's to organisations/give them a linage, its a easy high view source for fluff have this and that one come from the guys that give people powers but some of the less powerful variants have be cheap knockoffs by one of the street gangs extra and tie in all the unique ability ones you guys where talking about like freeze be linked to some particular hero villain event/organisation
its quick short pieces of fluff but people see them again and again so worth spending time to outline theme/feeling, like loading screens