Oh yeah? How many MAME emulators are on the app store these days? (or any other OS for that matter)
This will probably happen with another tablet before if ever it happens with an ipad, less restrictive OS and a simple USB port and this could probably be done tomorrow.
The patent they filed could just be used defensively so they have the option to create a 'peripheral with buttons and/or dpad w/ optional secondary display' which is all that patent looks to consist of - while stopping others from doing the same thing if they so choose.