default dotted quarter note in 6/8, 9/8, 12/8, etc

Do you mean just a different default duration selected when entering note input mode, or something else? If you mean what I think you might mean, it's possible shoogle's real-time MIDI project will yield a function to intelligently combine smaller durations (like a quarter rest and an eighth rest) into larger ones (like a dotted eighth rest) according to the time signature. But that would be an after-the-fact command you would run on rhythms already entered.

P.S. Compound.

I could imagien the default duration on entry to note input mode being made dotted quarter, but frankly, I wouldn't like that. If it's to change, I'd prefer it be whatever the denominator is - 8 in 6/8 time, etc. Or, as requested elsewhere, to keep whatever it is curre4ntly selected in the cases where it doesn't currently. Mostly, though, I think people should just be in the habit of entering the initial duration themselves, just as they do for all other notes. Whatever we guess is likely to be wrong often enough that I can't imagine why anyone would want to depend on it.

But I can also imagine wanting rests to be create properly accoridng to standard compound meter conventions while entering notes. That's an open feature request - see #4867: Rests in measures should be grouped according to time signature