DarkSword, I really admire your intentions here. Two quick points though...
1. There is a committed developer for the Myth series (existing games) - see http://projectmagma.net
2. The idea of proposing a Myth 4 to Take Two has been done. A group put in an exceptionally strong proposal with a very good storyline etc as well as technical aspects, and with low risk/cost to Take Two. Even though T2 _invited_ this group to put the bid in, after it arrived they decided they weren't interested. That's the main problem - Myth to them isn't a guaranteed money-spinner, in fact its the reverse. They won't go near a Myth 4 unless you can prove to them beyond doubt that they'll make a gazillion dollars.
Another option could be to make a Myth-like game. Not Myth as such, but with very similar gameplay, dev tools, an enthralling storyline etc, and on Windows/MacOSX/Linux. Released either as pay-if-you-like-it uncrippled shareware or perhaps as freeware. Its lifespan wouldn't be limited by how long it stayed on a store's shelves, and if it were high quality then it would grow and grow over time.
