My assumption is there will be at least something to the "home dock" portion, even if its simply providing more memory. How feasible would it be to have more GDDR5 connected this way vs. soldered on-board? Sure, more system memory could be nice, but what you'd really look for is more GPU memory to push up post-processing and maybe resolution. Maybe even a secondary CPU in the dock to offload some stuff to? Guess we'll see.
There has to be some sort of gimmick, or Nintendo wouldn't bother IMHO. Otherwise its just a slightly more functional Vita in being able to hot-dock.