Replacing Office is really the fatal blow, and that's where I wonder when we'll see someone like Dell or HP selling a cheap, business class iMac-like running Android on Arm in an effort to restore margins on high volume business channel sales. The obvious drop-in replacement in that case is Google Apps, and I'm sure Google would be happy to partner with an OEM to develop such a complete device.
The trick there is that the OEM needs to feel like MS won't or can't crush them. The aura of invulnerability of MS has to be broken, and when I look at the extended pratfall that is Windows phone and tablet, I can't help but think that OEM execs are feeling a bit drooly.