Honeycomb has been designed and optimized to run on the Xooms hardware, so I’d imagine that trying to run a larger and more comprehensive OS like Windows 8, patched and ported for a Tegra 2 platform would likely come at such a high cost in performance that any other advantages would be for naught.
While I would never consider trying to run Windows 8 on my Xoom, a bona-fide Windows 8 tablet will be a real contender for me in considering my next tablet device.
While the reality is that in order to provide me with usability, a tablet does not need to have the full functionality of (for instance) a laptop, but the closer a tablet can come to such full functionality (without impacting performance, and without being prohibitively expensive [i.e. the cost of MS Office vs the cost of Documents to go or Quick Office] to implement), the better and more attractive.
Of course, the other potential outcome of a viable Windows 8 tablet might be to push Google to provide the option of a less Spartan Android OS, perhaps providing downloadable and installable drivers to allow for the simple use of external drives and devices via USB, which would allow Android tablets to better compete with Windows 8 equipped tablets in terms of additional functionalities.
Actual “windowing” is, for me, an obvious advantage over mere task switching in Honeycomb, but given the availability of “clipboard” apps, hardly a deal breaker. Android doesn’t need to be as extensive as Windows to be an effective and “usable” tablet OS, but Google should strive to keep Windows 8 from having distinct advantages which might justify the additional costs.