Max,
The following is presented as potential ideas to overcome valid concerns.
... but could you also get all the props turning in synch with each other like a mechanical drivetrain would?
Each motor would be equipped with one, or more, encoders. These encoders, plus gyros and pilot inputs, will vary the power to each motor, as desired. If a motor starts getting too far ahead of the demanded requirement it can be temporarily made to act as brake by electronically turning it into a generator.
I suspect that aerodynamically the interaction between props and .... prop might cause some issues.
This appears to be the biggest concern, to date. As the craft maneuvers during cruise, the streamtube from the forward proprotor may 'wander' about the plane of the disk of the aft proprotor. An idea is to try and have the fore & aft proprotors in close proximity during cruise and spaced apart during hover.
Please destroy any of the potential solutions if they are not valid.
Thanks,
Dave