I wonder if the presto system is capable of actually doing this on a large scale?This is my thought process:
Tap on TTC bus = trip began in zone A/B.
If there isn't another tap on another transit vehicles outside of zone A/B. You'll be charge the base fare for zone A to B.
The system will have to know the TTC route you tapped on only travels in certain zone(s). For example, 37 Islington only travels in zone B. Tap on 37 Islington, and then a MiWay bus = zone B to C.
With this set up that'd be no need for tap off (except routes that cross multiple zones), because next tap on acts as a tap off for the first trip.