Wait - how in the world is a bluetooth keyboard not be compatible with Android 4.2, iOS 6, etc? [1] Isn't a bluetooth keyboard, a bluetooth keyboard? Is "support" defined as "exactly what is says on the label" (months of battery life), or "pairs; keystrokes appear on the screen"?
(10 minutes later of googling later)
Maybe I have partially answered this for myself: This claims bluetooth LE (4.0), and these are the OSes that "do not support it". Question: Is the 4.0 Low Energy mode "exclusive"? Can 4.0 hardware talk to 3.0 devices, even if they draw more power?
(to the wikipedia stations)
Bluetooth Smart is not backward-compatible with the previous, often called Classic, Bluetooth protocol. The Bluetooth 4.0 specification permits devices to implement either or both of the LE and Classic systems[2]
If I know Microsoft at all, this will be exclusively LE and it will suck. If you claim "months of battery life"[3] you can just as well throw in an "unofficial" fallback mode to the classic stack to make it work with, oh-only every device built since the late 90s, even if it is "weeks" of battery life.
It is just like MS to introduce an artificial limitation of only talking to 2012+ stuff for no reason... ("almost there"). Although I genuinely hope I'm wrong.
On the plus side, if this is the case, I would stake a considerable amount of my fortune (let's call it $10) that within months of release, some chinese manufacturer will come out with a close-enough version of it which will play with all the bluetooths, even if "accidentally" (older chips being cheaper). That will be a laugh and a definite purchase, and that will make this rant relevant, because I'll be all clairvoyant-in-the-downvotes.[4]
[1] http://www.microsoft.com/hardware/en-us/support/compatibilit... then select the UFK from the dropdown. MS, where's my permalink?
[2] http://en.wikipedia.org/wiki/Bluetooth_low_energy
[3] Not holding my breath about this. We'll see.
[4] Parting thought: Bluetooth is as old as USB. That blows my mind a little.