I was going to put these comments in last night, but opted out when we had a nasty thunderstorm start to roll through. Some of those thoughts have already been touched upon previously in the thread, but I'll try to make them articulate:
1) As an IP line other than M:tG, the Forgotten Realms is probably the most valuable asset that WotC has. This must be accounted for in any planning & discussion.
2) Due to the extensive publishing about the Realms (through novels, computer games, and RPG products), there exists a sizable number of gamers (myself included) who feel as though there is no room for making it one's own. Said differently, I would not choose to run a game in the Realms because the odds of somebody telling me "No, it's not like that" are perceived to be extremely high.
3) I concur that at least one initial setting needs to be fairly generic, with lots and lots and lots and lots and lots (have I made my point yet?) of room for people to feel free to wander around in it without worrying about being told their wrong. From my BECMI/2E/4E brainspace, there appear to be 3 settings that I think could fit the bill:
3A) I'm just too young to have had any real exposure to Greyhawk, but the gamers I know who are enough older than I am to have played in it tell me that it fits the bill here
3B) As somebody noted above, I think that Mystara, possibly with a bit of rejiggering to make things feel slightly more coherent, would fit the bill quite well.
3C) If it could survive the transition from 4E, I think the Nentir Vale would also work.
(Note: my gaming is on hiatus, so I know absolutely nothing about Golarian other than that it's the setting for Pathfinder.)
4) The part of me that grew up in the 2E era appreciates the plethora of worlds released during that time, even if some were better than others. To that end, I'd like to see at least some support for more than the default setting. I think the 4E model was close, but that Campaign Guide / Creature Catalog / tile set / 3 adventures (rather than 1) would come closer to the mark.
I'm not sure what the reality is of the status for the Dragonlance IP (who owns it, what pieces are licensed elsewhere, etc.) I agree that it's got the library present to support an introduction to gaming. Dark Sun can capture the post-apoc vibe, especially if allowed to really push some of the things I remember the 2E boxed set trying very hard for (e.g., playing up the defiler/preserver split and the possibility for any political message that might be present). Of the other major lines I recall from the 2E era that haven't already been mentioned, Spelljammer is too niche; I don't believe that Birthright covers a sufficiently broad spectrum of play; Planescape needs the foundation of at least one more setting to build upon (IMO); and I don't know enough about either Council of Wyrms or Red Steel to contribute usefully to the discussion.