Destructoid managed to siphon some information from a new Microsoft Expert Zone retailer quiz that focused on the optional content BioWare intends to make available for Mass Effect 2.
It lists, specifically in the Xbox LIVE Features section, (planned episodic combat via DLC,) weapon and armor packs, new downloadable characters for the (campaign experience,) new downloadable worlds, as well as (full campaign expansions for download.) I just can't wrap my head around developers planning DLC months or even years in advance. Remember when all this content was either included with the original game or carried over to an expansion/sequel?
It also mentions that the game will carry (periodic updates,) which features DLC, via Mass Effect 2's unannounced in-game (Cerberus Network.)