-we could separate driving assists and maybe telemetry from AFGearVehicle class but i do not think that it would fully prevent your inheritance problem.
-we will look into the physical material and the skeletal mesh component issues.
-replication and backfire are in our todo list.
-unfortunately these extra platforms require a lot of effort to support and we do not have the hardware for mac/ios and we have little to no experience with linux. i believe you can manually compile the source for any platform since there is no external dependency except a few unreal plugins.