This will never go anywhere.
The main reason being that the hardware peripheral support wil be totally out of whack (video cards, media drives, etc.). Apple has complete control over such things, so it's fairly easy for them to virtually guarantee compliance and operability. PC users are still plagued with major headaches for such things. To add an emulator on top of that can only mean trouble.
For example, I want to see someone use Toast via the emulator on an uber-cheap CD burner. Or watch their video card give the emulator's OpenGL fits. Or try burning DVDs with iDVD or DVDSP. Or print to a parallel printer.
The other reason this will never go anywhere is that there simply is no demand for this product. Yes, there are really compelling products/software these days for the Mac exclusively (Final Cut, iLife series, Motion, Shake, etc.). But you're not going to want to emulate those things. Additionally, those apps tend to be for users that actually make money with them, therefore they can easily justify the expense of buying a real Mac. Kepp in mind, we Mac users typically run VPC because we HAVE to, not because we want to. Admittedly, multi-platform testing is a very legitimate use of an emulator. But I just can't believe there is enough interest in, say, making sure the web page looks right on the Mac, to suport such a product.
Another reason is licensing. I don't know how all that works, but I've got to believe Apple would crush this product like a grape if push comes to shove.
Having said all that, if by some miracle they can actually get this emulator to run just as well as running it on a native box, and Apple lets them do it
well then, that's whole different ball game. Too bad it will never happen. Ever.