Buying a device and controller doesn't work so well. Gaming battery life is significantly worse with a tablet, the Shield's batter life alone makes it worthwhile. There is input lag with bluetooth. Gaming clips or attachments are also very clunky.
A Dreamcast emulator would make the Shield perfect either that or Sega ports Dreamcast games to Android (possible but not likely). Need my dosage of sonic adventure. I see no reason why the Shield Couldn't run a dreamcast Emulator flawlessly. Hopefully Nuldce is completed or Lxdream is ported...
If you need a physical keyboard so bad there are options available like this http://www.amazon.com/FE01-BL-Wireless-Keyboard-Mouse-Touchpad/dp/B003UE52ME/ref=sr_1_2?ie=UTF8&qid=1377704300&sr=8-2&keywords=mini+bluetooth+keyboard and...