I wouldn't ride anything but Di2 on my TT bike. Besides the situations you've described, if you have a traffic / obstruction issue where you have to jump quickly to the brakes, the dual controls save you a lot of time getting back up to speed. Generally, if you've got to do a rapid or emergency stop, you also need to shift way down at the same time. With dual controls, you can shift while braking in that circumstance and avoid several seconds delay.
And besides . . . shifting with Di2 in the extensions is a lot easier. Just a mouse click. You don't have to change finger or hand positions to make any shift across the range.