The way Hot War handles NPCs would make it an excellent game system for running Britain vs. Russia in Afghanistan!
The PCs are all British agents like Kim in that Rudyard Kipling novel, and their files are being reviewed. The players use their PC relationships to identify the contacts they've cultivated, the other agents they know, rivals, enemies, etc.
OK, on topic, I think I'd like to see someone new take a stab at parallel universes, a la Cross-Dimensional Teenage Mutant Ninja Turtles (or Rifts), or Alternity Tangents, or even Planescape. I always wanted to do a Time Bandits RPG, but I couldn't figure out how to properly randomize the next portal opening.
I've got TFOS, and it defintly has its moments. For a game that first appeared in the late 80s, it has some intersting indie design features. For example, Xp is handed out via voting, and characters can't die, to encourage more comical injuries.
Speaking of which, Toon might also be over due for a new edition or clone. Cartoon Action Hour handles dramatic settings like GI Joe, and there are a number of Anime games (BESM, OVA, BountyHead BeBop, Random Anime, Mekton...) but not really anything for the old Merry Melodies/Disney Shorts.
Suddenly, I'm inclined to collaborate on a Wille E Coyote/Tom & Jerry game. No idea how that might work, since someone is invariably going to be unduly tortured - but its an interesting thought exorcise. Perhaps during part A you earn verbs/nouns or XP that can be traded for such, in part B you string them together for the most Rube Goldberg chase scene you can think of?
Back onto the topic of retro-clones, how old does the game have to be for this to become a consideration? Supposedly a new edition of Mekton is in the works - but there has really been any material since 1996. CyberGeneration is from 1995, though the semi-related cyberpunk 2020 line got rebooted into its 203X incarnation fairly recently. (2005, though that kind of ret-coned C-Gen out of existence.)
Of course it might not be a matter of age, but rather a certain ethos the game expressed. "" approaches this thought on the D&D crawl basis. If so, then we might want to make a list of games with a palpable spirit.
One last suggestion for retro cloning - games where you area a character playing a character. The old titles Dream Park and Hong Kong Action Theater where you are a partcipant in a holo-deck style LARP or an actor in summer movies comes to mind.