It's clear to me, that the IC would be most active in new holds, like Whiterun. As the faith of the Nords and the IC are so similar, I don't see them having a missionary role like they did in Morrowind, where they were on the frontier, surrounded by heathens. It seems the IC would be most active in The Reach. The gods of the Reachmen are considered particularly barbaric and pagan by civilized peoples, and we could have some quests centered around a mission to convert some Reachmen tribes. The other mission should be to care for the poor and sickly, something that would be a busy job in the most metropolian cities, like Haafingar and Karthwasten.
Currently we have cult shrines in the following locations:
- Karthwasten (large shrine with all deities)
- Markarth - Arkay shrine
- Fort outside Falkirstad
- Fort south of Karthwasten