I would like to see a turn-based RPG with the rule set of d20 Modern, or the supplement d20 Future. Those would open up a huge amount of options, like a planet-ship that holds billions of people and many different types of weather conditions. There could also be a campaign set in d20 modern where players work for a secret organization, but something along those lines, that uses the d20 Modern/Future rules, instead of a run of the mill D&D fantasy world. Lastly, I wouldn't mind a steampunk genre game, but not like Arcana, something different, magic is simply glorified alchemy, there is clockwork machines, and steam powered weaponry. You know, all the good stuff.