I think we can differentiate between “maker projects” and real products, although certainly sometimes there is crossover.
So I think for one’s personal project, certainly it can sometimes be about pushing the envelope, but sometimes it can just be for other reasons like learning or just because.
So I don’t really think you need a custom BLDC motor with diagonal magnets (even if it would be better). I think you could take a crappy servo, change it over to continuous rotation, add some more gears and see how it goes… going for a BLDC is anyways going to make it a cool project 
Real motorized camera lenses anyways use different motors like ultrasonic piezo motors to achieve their super fast movements in the narrow space around the lens.
I do think, like Valentine, that the 19000KV drone motors won’t really work for your application, and will be hard to control with FOC due to their high speeds.
But I think any kind of gimbal motor will work from the electric and control point of view, and it’s just a question if it will work mechanically in terms of friction/torque.