How would this (NES emulation) even be possible, though?

Is the OP asking to use the keyboard (difficult with tiny keys, not to mention "multi-button" presses like a diagonal movement on the d-pad)? Or rather, the touchscreen? (Awkward with no tactile feedback...)

Unless we're talking about some add-on controller that interfaces through micro-USB, I just don't see how this would even be enjoyable.

And like others have said... let's fix the things the Pre is SUPPOSED to do, before adding on things like this that have a niche audience.