> Best case: you make a ton of money by selling to actual businesses (rather than annoying geeks and other weirdos who dare use uncommon clients); slightly-worse case: you sell it to MS.

And worst case: MS change how things work and block this sort of thing happening again. You now have a bunch of angry customers with a hack that doesn't work.

I'm no lawyer, so I'd also check the legal implications of selling something that builds on top and modifies Microsofts application without their explicit consent.