Seriously, could Apple do this, given that here are now Intel-based Macs? What about home users? Real competition for MS - that would be fun!
To make it an off-the-shelf boxed product for the
mass market would be a huge project for Apple, to reduce that mass market by a very strict "compatible hardware" approach would reduce the scale of the investment but still be a huge undertaking (i.e. very expensive) for a much reduced potential market. Also considering that the "mass market" just doesn't upgrade anything in the box they buy from Dell or PC World what is the potential market even for an off-the-shelf upgrade?
The other route would be to offer it as a
pre-installed product (perhaps via a "certified" hardware platform) and that would be considerable less expensive however who would pay for that - the PC manufactures i.e. the likes of Dell or Apple themselves?
If it is Apple can they make enough money from the very small margins PC manufactures have to pay for the pre-installed software? It would mean huge new support costs and headaches for Apple and any PC manufacturer who went down that route. (Plus see the "on the day" price comment below.)
If the costs of "hardware certification" were to be borne by a manufacturer like Dell I suspect it just couldn't be made to work given their current business models. (Given the very idea of a "certified" hardware platform is entirely the opposite to how a company like Dell works e.g. their flexibility with components to get the best "on the day" price).
Also then factor in the competition this would cause for Apple own brand of Intel PCs.
All in all whilst of course possible I suspect it is something that is not very likely, at least in the near future.