Fermata, rubato ....
Just thinking aloud here... Would anyone else find it useful to change the tempo of a single note or chord? Not to enter a tempo change so much as to just add a little rubato or modify how long a fermata is held. I welcome ideas, but I propose, when a note is selected, using the "<" as a shortcut in note entry to add 1 bpm to the tempo, and ">" to subtract 1 bpm from the tempo for that note only. This may seem counter-intuitive, but I think it is not since the < would make the note come earlier, and the >, later. Maybe a little pop up like is used for roll-over help text could display the value of what was entered when the symbols are pressed, ie. 0 for a note that is in tempo and -8 for a note that is slower or +10 for one that is faster than tempo.
Of course these changes would need to be automatically applied vertically to all parts of a score, whether or not they contained a note on that beat. I guess it could be summed up as just a quick and easy, temporary tempo change.