I think incompatible scales are a requirement of franchise wargaming, 79th--which is why I mostly don't do it. I'm sure there are some fantasy rules not produced under license from a media company which will cover combat in Westeros, should I be interested. (I covered I think four volumes of Martin and never found a battle as interesting as some of Howard's or Tolkien's. Martin did interesting stuff, but not interesting mass battles.)
And weren't there recently two Star Wars miniatures games, complete with incompatible scales?
What, really, do we have for "IP" options? Probably Martin and Tolkien for fantasy ground combat, with Howard a very distant third, Drake, Heinlein and Star Wars for SF ground combat, and Star Trek, Star Wars, Galactica and B5 for spacecraft. I think there was a short-lived effort to do something with Cherryh's "Company Wars" and you could do something with Drake's RCN stories or the Honor Harrington books were someone so inclined.
Myself, it doesn't seem worth fooling with on the ground. Buy the figures if they appeal, and use rules not written by people trying to sell figures. Space combat might be different, given the different tech, but the stuff comes and goes so fast, I'd try to buy all my toys very quickly.
