Well the Teensy 3.0 is already half that requirement.
That's true.
I guess the problem with on-board buffering is controlling the IO features on a pin-by-pin basis. For example how do you have pin 1 as an input with pullup and pin 2 as an output. And that's not even thinking about the analog IO.
its the programming that worries me....
I haven't used any but AFAIK many of the current environments have that covered in an Arduino-like manner. So that shouldn't worry you too much.
Rob