I realize that there is a mandatory install on the PS3, but does anyone know if there is going to be one on the 360?

it wont be mandatory but it does speed up load times by a few seconds

Does the 360 ever have mandatory installs? I own one and have never run into a game requiring it. I install all my 360 games anyway while I play them. It prevents disc read errors, improves loading times, and saves your optical drive from going bad from wear and tear, the leading reason consoles break down.

I have had my disc drive break twice before I got anything else wrong with it. Its a good idea to install but not needed.