I don't see how it can easily know what the next letter of the alphabet would be.

True, but it might be possible for a user application to let the user scroll through the letters themselves, I dunno, using the knob maybe... And said application could inject the corresponding IR code for that letter when it's selected. It wouldn't be strictly "next letter / previous letter" but might be even more useful, as you could go from the A's to the Q's faster, without having to go through the B's, C's, etc.

liquidiq & TheTwin314, would this be an acceptable alternative for you guys?