People have certainly mentioned this before, and it would really be a neat idea, but I can only speculate as to how difficult that would be to manage. Heck, the gyms just near me are changing hands constantly - at two in the morning, mind you! It'd be a great way to increase the competitive factor, I agree... but by the time you check the website and get to that location, it would have changed no less than three times, I imagine.
Still. Having a map of stops and gyms would be convenient, even if it somewhat spoils the "exploration" feeling GO is supposed to be all about. Many different people are compiling lists and making maps; we even have a list in the making
here.