Hopefully they will drop some of their asinine backwards compatibility with everything from King Tut's day up until now. Forget anything before XP and let's roll with it. That would cut down the size of it considerably. It would also rid it of a lot of holes and vulnerabilities right off the bat.
Make it modular so that you only use what you want to use, not what some pinhead in Redmond thinks we should use. And give us the option to make it as secure or unsecure as we prefer.
While they are at it, they could make the blasted thing affordable! You can buy legit copies in China for dirt, but only because MS wants them to use it and not pirate it. Here you have to fork over an arm and a leg.