Hi William,
not a bad solution. I am not certain how much realtime it is possible to get directly out of a pi.I my company we use kuka robots. Everthing runs on a single pc with vxworks and windows.
I would believe a pi with an axis controller software on it and another pi with an userinterface could also be nice.And 99.9 % realtime. It is worth to test it. 🙂
CU Oliver