There's already a universal system that's been out for quite some time: Steve Jackson's GURPS (Generic Universal Role Playing System). They have a ton of source books out for it, though all you really need to get started is the basic rulebook. It's a very flexible system...it's what I primarily played back in my pen-n-paper RPG days.
Yup, I know GURPS, this is a different system. It is designed as a completely online rules set. It will be marketed over the internet, with a free core rules and a fantasy world being available, and then the customer purchases into various expansions. Initial marketing is as a pen- and-paper system, but the end result will be as a equivelent online system.
My main job is world creation, so there is at least some attempt to make the world believable, I get to use my background in biology and anthropology. I also have had alot of input into the combat, weapons, and armor systems to bring them more online with real-world historical examples.
Lamont