As stated above, these are used for low force and typically low accel rates. Yes the cable can stretch. If you require more accuracy you can use a seperate measuring device, readily available and relatively inexpensive.

I doubt a $50/axis machine will be expected to deliver extreme accuracy.

The radial (side) force can be canceled with an outboard radial bearing.

These cable drives aren't intended for high precision, heavy machines or fast machines unless they are very light.

Besides, this isn't new, there are many applications out there already, some many years old. Some even older than me and I'm older than Adobe and he's older than dirt. lol