Star Fox x Mass Effect - Star Fox games really can't be all about the on-rails combat anymore, and previous Star Fox games have all sucked on land. Meanwhile, the Mass Effect games do ground combat well, but haven't really done anything else. Bring the two halves together, and you might actually have a decent combination. Plus, with how vast the Mass Effect Universe can be with all its alien races & cultures, it wouldn't be that out of place to have anthropomorphic foxes and toads running around with humans.
Of course, EA owns Bioware so that would never happen given EA's stance on Nintendo, but it's a nice dream.