Pocket-Lint had a bit of a chat with Microsoft's UK top man, Ashley Highfield.
Apparently, there is no plan to do a tablet OS until the company can come up with something to distinguish itself from the competition. That's fair enough, though I think it's better to aim for usable, rather than just 'different'.
"This just in: company refuses to shoot itself in its foot; and in related news: company plans to produce useable product!"
Let's just assume common-sense is at work here, shall we?
Tablets require different UX's - hopefully noone thinks there's a one-size fits all. For that matter even mainstream operating systems could use new UI metaphors. We've been stuck with the same basic UI metaphors for ages, with only minor revisions. Surely there's room for improvement between here and Minority Report without too much ingenuity needed. Also, Android is doing some good things in the UX space (as is WP7), so I can't imagine the next version of Windows in a UX status quo. The new taskbar is nice, but still a minor revision on my oppinion.