In terms of OS for an x86 tablet, you're looking at Windows 8, or Linux with a custom shell, and that's it. There's an unofficial x86 port of Android, but I wouldn't stake any real product on that without any support from Google.
Since MS has already established the baseline price for the Win8 tablet around $800, and they're marketing it more as a tablet PC that can do everything you do with a normal desktop or laptop than an iPad, is this really that much of an issue?