Pricing is going to be key. If the lowest price tablet is $500.00, it is going to be very difficult for microsoft to get into the market. It seems they priced windows 8 right by allowing users to have a $39 upgrade and the fact that it looks like it will be fully integrating to the PC is great. Microsoft has alot riding on this but the right moves could open the doors to other things.
For example: I will eventually upgrade my PC to windows 8. If I can get a cheap windows tablet, I could sell my android tablet and get a surface tablet. Then when my phone contract comes up (if I happen to really like the Metro UI), I could possibly get a windows phone. Then, when then next generation of consoles come out I would probably favor the microsoft console simply because of the integration (I currently own a PS3).
So technically, microsoft has the ability to sell me 4 different items but the main deciding factor will be the quality of the OS and how integral it is to other devices, and the price of the tablet.