It's a good idea but it might conflict with text (object) selection. I'll use different terminology:

tap-and-hold (1/2 tap) is for popping up a menu
tap is for activation
tap, tap (double tap) is for quick zooming
tap, tap-and-hold (1 1/2 taps) is for text (object) selection when contextually appropriate

So, maybe the zoom circle could appear with a tap, tap, tap-and-hold (2 1/2 taps). It would only be a 1/2 tap further than the quick zoom.