If you do want to use a keyboard with the iPad, you can buy and use the exact same bluetooth keyboard you can use with a Mac Desktop or Laptop.
The Surface keyboard covers show the kinds of compromises that Apple probably wouldn't make. The touch cover is a decent cover, but suffers from the same hovering hand-strain issues that make on-screen keyboards unpleasant to use. On the other hand, the type cover is a poor cover, in exchange for a slightly better keyboard.
At this point, I think a converged device would only hurt Apple's profitability and brand. Why would you buy a Macbook and an iPhone if you could get away with just one? Plus, we'd have to deal with the differing instruction sets. (It's one thing to write an app targeting mobile and compile it for ARM; it's another to suddenly expect 3rd-party developers to start cross-compiling desktop apps for ARM and phone hardware isn't fast enough to emulate Intel chips the way Intel chips emulated PPC during the last architecture transition.)
I know Microsoft has been trying to appear more vibrant with their university recruiting efforts; they often play up the opportunities to work on Windows Phone and XBox. At the end of the day, though, developers there still have to deal with the bureaucracy and code that hasn't been touched in decades. Microsoft has often been one to explore new form factors (Windows CE; XP-based tablets, XP-based media centers), and I'm sure they still pour lots of R&D into it even today. Making products that are good enough for users and priced low enough for people to buy them, however, is still a challenge, I think.
