Although, Shadzar mentions something interesting...

I have to quit doing that!
Playing through the changes of the spellplague actually sounds interesting, and could be done starting from ANY edition pre-4th, moving through to the story that was caused BY 4th, but not necessarily using the 4th mechanics anywhere.
Would give those people hating the mountains of canon their chance to do away with lots of that canon, by their own hands. For me, just be fun to see what would kill the Seven, Elminster, etc. while playing it out. But would many see it as just another Time of Troubles?
And FR due to Realms-shattering events is likely more than just 2 settings.

But that is a discussion for the thread about fragmen....oh wait, that is
this thread.
The only ones to care about spellplague stuff are forgotten realms player who still believe that they must follow the lore or else they get eaten by a grue.

...or the ones that, I don't know, actually liked the lore because the world had a wealth to use and you could plop a game session down anywhere and have little work to do to find something for the players to do as opposed to having to come up with your own cities and stuff if you were busy.
The problem was never the people liking the canon wanting to use it, but the people not liking it, just ignoring it. Don't like the Harpers, remove them...
Its when the two played together the problems come about, so don't force others to paly a game they don't want, let them play their own, if you end up with two groups of players with not enough to play a game with, then pick another setting to play in you CAN agree on...since there are like 300 of them.