The wait time wouldn't have to be excessive. As a real world example, the default double click speed in Windows is 500 ms and that is pretty slow. I'd imagine that double tap would actually be faster than hold since the wait period stops once you hit the second tap though it could potentially slow down single tap (since the upstroke on a single tap cancels the hold wait period but wouldn't if waiting for a double tap). Put it on the F-switches only and any delay wouldn't usually matter since those switches aren't typically configured for fast changes anyway.
Also, the delay to wait for the second tap would not be necessary if the single tap triggers non-destructive behavior that's overridden by the second tap. In that case, the first action would happen immediately on the first tap and then the second action would take place on the second tap.
Quite a few loopers work exactly like this so this is not an unfamiliar concept to guitarists. For example, according to the Boss DD7 manual, it actually has a 1-second delay to detect the second tap which stops playback/record but you don't notice this because the first tap engages record/overdub/play immediately because the stop simply cancels the record/overdub/play.
Imagine having one switch that can do this:
- 1 tap: Looper record/overdub/play control without entering looper control screen.
- 2 taps: Looper stop without entering looper control screen.
- Long hold: Display the looper control screen (or looper undo like the TC Ditto's).
It's not hard to imagine a ton of use cases where a similar pattern would be useful. XY switching maybe? For example, single tap turns block on in X mode, double tap turns block on in Y mode.
Obviously, this all could be configurable so advanced users could access the functionality without forcing it on anyone.
In general, I have two Boss footswitches attached just to access some of the extra switching functionality in the AX8 and it would be nice to not have to use up the pedal board real estate for that. I see in a lot the rig pics that others do the same thing.