An idea that occurred to me as a kind of compromise between the 10 minute short rests optional rule in the DMG and the 1 hour short rests that are the default.
Have your short rests initially only take a few minutes, but each additional short rest takes longer and longer until you take a long rest and the short rest duration resets.
Example:
1st short rest: 15 minutes
2nd short rest: 1 hour
3rd short rest: 4 hours
4th short rest: 8 hours (at this point you just take a Long rest instead).
The idea being that it takes longer and longer to recover as your day of strenuous adventuring goes on. Also limits "short rest abuse" that some abilities are prone too.
What do you think? Useful, or doesn't add anything to the game?
On a day with two short rest, you effectively help class with short rest refresh. Is that your intent?
3 short rests adventure day are rare at my table. And with that mechanic I would prefer a long rest instead of a 4 hours short rest.