Funny how this thread's titled "crossovers that'll never work" and there are some legit ones here. Here's my crack!
Quest for Glory VI: X-traterrestrial Action (look the series never had much consistent subtitling okay?)
How would you mesh a heroic fantasy with a gritty alien invasion simulator? How would you balance character imports and how frankly OP the Magic ability is (especially on the three classes that don't have it by default, and
especially on the Paladin) without trivialising the strategic and tactical parts of the game? Hell, half of the wives you could have by the end of Dragon Fire could be considered so OP that they should have Geoscape abilities! As in, instant mission deployment with no ship, full healing in both Geo and Battlescapes, shooting down a battleship with a few clicks or pacifying a Terror Mission so effectively you get free research kind of powerful. Then again, OXCE supports mana now...
(but not a full suite of intrinsic abilities that could be used for learned spells - I'm sure you're limited to one special intrinsic weapon without using hand slots)
Anyway, it would probably have Weirdlings and the aliens from Space Quest (being a Sierra game and all) - and knowing their sense of humour, you'd probably need Roger Wilco to save the Earth/Gloriana, having to first figure out how to get him out from wherever he is in space, time, and sequels. And even with the power of X-Com and Devon Aidendale at your command, the final mission would just be defending some VIPs for a set number of turns before Roger manages to press the self-destruct button on the super toilet housing the gaggle of galactic insurance salesmen.
Song of Ice and X-fire.
Seems more like a total conversion than a crossover. Perhaps if those were the enemy factions and you played as X-COM somehow? Put you in mostly the reverse position of your technology being superior to the enemy's (although not enough to be a complete walkover - consider the absolute force of a bullet compared to an arrow or bolt), but you still needing to do research to learn all that magic and how to tame dragons and junk.
