I'm going to stick my neck out again and risk being shot down by 40k fan boys ;) . But I really would love to do a Skaven 40k army.
* They already have the miniatures to make creating this army possible.
* They have the technology to create mech, power claw, warp lightning cannons etc..., and they have cool gods demi gods, daemons and mutations.
* They also have the ability/technology to create a warp rift, probably by accident(details can be worked out later), which could warp them into the 40k universe. ( i found the perfect planet for them to land on and wrote it down somewhere, will try and find that again
* The possibilities are endless and there are already some very 40k ish minis available for them.
space rats FTW
note these minis are for a bloodbowl team, but you get the idea :D