i just want to toss one interesting link in here. the guy over at

http://redbrickgames.com/blog/

is working since 2005 !!! alone on an rts and is so far the only person i know of, that came this far. you get a good insight of what its like to develop this kind of game while reading the blog. bear in mind this guy is an experienced programmer c++ and still has lots of problems to solve everyday.
if i remember right he even used parts of the torque rts starter kit...

edit: ohh and damocles i really like your idea to create this rts maker, i guess if you do it right it could be quite successfull. with 'right' i'm thinking of a good basis but still beeing flexible enough to customize things like a.i. if you want to, so every game made with it can be different not just by the looks of it.