It is possible to .join and ride along, but you can't fly. No one dies trying to learn how to fly AHII, true, but in my opinion, a dual control plane could help some people get over initial learning problems.
Plus it is a novel concept that purely on its own would likely draw interest.
Personally, I don't see how internet speed could cause any problem. How much time would it take once a key is clicked to switch control from one pilot to another, surely not even 1 second on the internet. Discos happen, but meh, not all the time. If someone discos the other pilot could automatically get control, and if it's the cadet, oh well...
Use some key combination like SHFT C and SHFT I to change between Cadet and Instructor.
Add a small panel with two lights clearly visible, (cadet) - (instructor), in the cockpit of the Stearman or T6, then either one of the two pilots could choose who currently has control of the plane.
Players can already become gunners in bombers, meaning two players are already playing from a single plane in game.
Beyond that, the dual pilot concept might be added to bombers, to let a real pilot and co-pilot share flying time.
There are a lot of reasons for flying AHII, including online camaraderie, not just boomin everything in sight in late war hot rods. Dual control planes might be worth the time of developing.
Best.