7" Windows tablet - where is it, and what should it run?

To me, the 7" tablet is the form factor that comes closest to "indispensable" in the tablet category, especially as price and ergonomics come into play. Witness the Nexus 7, Kindle Fire HDX 7", and the iPad mini - all very desirable and useful, and in the case of the first two, eminently affordable. So it seems odd that there is no Nokia or MS (nor any other Windows) entry into this category (that I know of). Especially when Nokia is making a gigantic phone that, IMO, just wants to be a small tablet, and is also making a large tablet that costs over $500.

This also raises the question: what would such a device run: WP8, or RT? What would you prefer? Would there be a performance or price difference between the two? I would prefer WP, but I don't use XBox and don't need it tied in to my home entertainment. WP seems lighter, cleaner, has the app selection, and generally seems more appropriate to the form factor.

My apologies if I'm missing some device that's in the works. I know there's an 8+ inch Lumia coming running RT, but I still think it's a little awkward in that it's too big to fit in the palm of your hand but too small to meaningfully use RT for a lot of things.