As long as it was a once off session, I can't see anyone objecting to it overly much. You'd have to be a bit 'precious' to be so against it, you'd storm off or complain bitterly about something like this, even if it was a genuine bait and switch.
Now if it was a permanent change that was never discussed with the rest of the group, then I could see justification for being upset. But as a once-off, I think this is a great way to change up the pace and throw the players a curve ball and would make for a fun session.
Wik, that is really cool.
I wouldn't have made a post except I can't rep you right now.
So they'd roll up different characters for each age/game type, or would the same set of PCs time-travel from age to age?
And how much adventuring would they do in each age/system? Just a one-off adventure, or enough to gain a few levels, or ... ? I ask because I'm wondering how much character continuity there'd be for the players if they're generating a whole new one that frequently..particularly if they happened to really like the character they'd generated in one of the systems.
If it was the same set of PCs time-travelling forward through the ages and getting re-skinned to suit each edition, that could really rock. (though it'd be a lot of work...)
Lan-"or the 3e guys could meet the undead remains of the 1e guys"-efan
IMO, a "bait and switch" would be "make up characters for a CSI-style game" and then having Cthulhu apocalyptize the world in the second session, throwing the PCs into a survival horror game set in the world of Thundarr the Barbarian, for the rest of the campaign.
What I've been most impressed with about Gabe's DMing is how willing he is to completely step outside the box for a session, often creating some pretty nifty, unique mechanics in the process, without tying his campaign down with permanent houserules.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.