Regarding one-to-many... I'm just about to begin writing a one-to-many notification system, to deliver content to an arbitrary device (SMS phone, pager, email, etc.) The idea is that content producers shouldn't have to worry about what device a user has, how many devices they have, or where they want to receive content. I'm not sure to what extent I'll be able to integrate it into ACS... it's a rewrite/redesign of a system I had developed independantly of ACS sometime ago (never did like the naming conventions, hacked code, etc. of versions 1 to 3).
