My understanding has always been that the Wii U should be capable of playing a Dreamcast emulator at decent speeds, but it would take some serious optimization from someone truly dedicated to getting it to work on the system. No one has been working on such an emulator on the system as far as I'm aware. So don't exactly hold your breath on it, but stay vigilant all the same, your request isn't without merit, maybe one day such a thing could drop on the Wii U or maybe not, either way I wouldn't anticipate it happening anytime soon.