@Alexander_Pritchard I haven’t even started to look into it, but DC servo motors seem to have a few advantages over steppers like a more flexible speed curve, higher speeds and being able to control torque for example. (And yes, they have disadvantages too like being more complex to control and more expensive). But there must be a reason that big robots use DC servo motors and not steppers ;).
Closed loop can prevent a failed print on non-mechanical problems: accidental incidents when the printer gets bumped. Some weak motors make this common but stronger motors solve most of this.
It also opens up a few nice features: shutting down the machine or in the case of a power loss, you could get your power back and continue a print- thus requires software of course. Also, tool changes get much easier- but no compelling case for this currently exists. Some flavors of multiple head extruders would benefit too, since precision is hard w switches. I know I’m reaching, but in the case of stripped filament, it would simplify detection and a solution to be triggered… maybe more compelling, it could offer useful feedback in cases where the filament isn’t stripped but the stepper is skipping… obscure, but dynamically controlling power to the motors would solve this… it’s not truly a mechanical problem, more like bad decisions in the firmware.
Ok I’m done 
@Thomas_Balu_Walter Hmm you can get a ~4kg torque digital servo from hobbyking for ~$9 that could be modified for constant rotation (you probably knew that though with how you are on flitetest videos a lot)
@Alexander_Pritchard I guess I am now and then ;). Digital rc servos still use a potentiometer to get their position. So making it a continous rotation one will remove the feature of the closed loop for positioning. Also I’m thinking that dc servo motors have a much higher resolution. But as I said, I have just read a bit about them and am more than far from being an expert.
@Thomas_Balu_Walter I wonder if you could replace the pot with a rotary encoder? They do have continuous potentiometers but they are more expensive