Good points. Agreed that
Oxford conversions were very tempting (especially in a straitened postwar economic environment). A problem for both future RAF contracts and dealing with the Brabazon Committee was that Nevil Shute Norway had made his disdain for the Air Ministry (and the shortcomings of officialdom, generally) quite public.
De Havilland definitely had an advantage with the
Dove. Some of that may have stemmed from DH's traditional advanatge of both airframe and engine being supported by essentially same entity. In the early days, Airspeed seemed glued to Armstrong Siddeley powerplants but the latter had long-since been gobbled up. Not a problem for
zen's scenario, though, so long as he doesn't mind his longer-lived Airspeed being a part of Hawker Siddeley Aviation.
Interesting notion about a 'next-gen' AS.5
Courier. NS Norway was obviously a
Proctor fan
The original AS.5 was that bit bigger and more powerful than the Miles and Percival progenitors. Perhaps maintain that size difference (for a 5- or 6-seater) but shift to all-metal construction?
The best of the 'Ox-boxes' was the AS.46
Oxford V powered by 450 hp P&W R-985
Wasp Juniors. Maybe offer that as an option on postwar
Consul conversions. Surplus A-S
Cheetah X radials could then be a 'budget' option for powering your '
Courier NG'. An alternative would be to go light twin - ie: a 5-seater but with two
Gipsy Majors instead of the single radial (so more Piper
Apache than Miles
Gemini).
As for having "to move into the jet age at some point", did you mean literally jet-propelled
zen? If so, what is your hope for outcome?