I'm a huge fan of games that suddenly start playing differently. And I'm an armchair game tinkerer. And I have a bookshelf full of decades of awesome Munchkin stuff. So, putting it together . . .
The premise: Start with Munchkin Steampunk. You all are steampunk munchkins, doing steampunk munchkinly things! Play as normal. Then, once a player hits a predefined level (I suggest 5, 6, or 7), things get weird.
How weird? Well, it turns out that one of those "steampunk munchkinly things" maaayyyyy have accidentally breached the time barrier, in a way that makes H.G. Wells rub his forehead. Shuffle Munchkin 10 – Time Warp into the draw pile.
From here, either play continues as normal (the "well, that just happened!" option), or – if your group wants a bit of extra spice and a longer game – the game only ends if the winning level is a Time Warp monster (that is, you need to beat up some hapless thing to help get you to your own era).
Will this variant work? No clue! I just thought of it, and immediately trying to implement any whackadoodle thought that springs to mind without consideration of the consequences feels both steampunk and munchkinly. If anyone gives this a shot, feel free to let me know how it turns out on the forums.
-- Steven Marsh