In all honesty, I doubt there would be very much demand for such a device.
Nearly all modern drives will accept step/dir as an option.
On machines with more basic analogue drives/amplifiers, by the time you factor in the cost of two/three of these, will it be cheaper than just buying a controller that supports +/-10V?
To put it in context, a CS-Labs IP-A unit is €600, which is only €40 more expensive than the IP-S (step/dir) version.
A Dynomotion Kanalog add-on for the KFlop is $250.
But both those options are also giving you high quality cnc controller with 24V compatible IO.
Even in the LinuxCNC world, MESA provide +/-10V cards for not that much more than step/dir cards.
Thinking you can convert an industrial machine cheaper to a high standard is a false economy. You still need to factor in the cost/hassle of converting/interfacing any logic to low voltage. Admittedly on a basic machine there won't be much in the way of logic, but there is still a cost of converting it.