Thanks! I'm also currently exploring drivetrain options. I know this sounds crazy, but I'm working on implementing an e-CVT like in the Toyotas, they are actually super efficient and very comfy. I'm not really a fan of hub motors, so I went with some smaller out-runners. Your project has forced me to resume my gearbox project now :)
There is - or was - a Finnish company doing precisely that. Google 'Revonte', amazing little product they made.