Not sure how feasible it would be but using the experiance from developing collets for the multi drive could one be developed to take tapping bits and have a standard hex shank to fit into the pocket driver? The pocket driver can then provide the torque to cut the thread but also enable threads in small spaces where a standard T handle would not fit.
McMaster-Carr sells hex-ended tapping threads, but they all seem to be for power tools w/ chucks — I would also worry about the asymmetrical shape/bar of the Pocket Driver (and larger Metmo Driver) making it hard to maintain squareness/verticality.
A tap handle is a pretty small tool, and the good ones not so expensive that one can’t afford all the sizes one might need (says the guy who still hasn’t found a vintage Starrett in a size and at a price he can justify) — this is complicated by my lusting after:
(which if anyone has experience of, I’d be glad to hear their evaluation)