The one system that i’d love to see that has never been done to my knowledge would be Blake’s 7
Then again Buck Rogers in the 25th century needs some love too
And of course Elder Scrolls would sell (I’m sure Todd Howard wants Skyrim done in pnp format as well)
I could get into a Blake’s 7 setting, or B7 inspired setting myself.
There was a bootleg Chaosium system Blake’s 7 produced late last century
I would love to see games for Phoenix 5 - ultra-cheap Australian answer to Star Trek which needs to be seen to be believed.
Oh, and of course Raumpatrouille