I have 2 road bikes from the mid/late 80s with internal rear brake routing.
both are pretty easy to set up. Just dont pull both the cable and housing st the same time. Keep on in the frame at all times and the other routes easily.
These are both full housing.
on the frame i built this winter, we set it up with internal rear brake housing, but with cable stops. The bare cable is routed inside the top tube with a thin tube of brass thats brazed to the cable stops.
its fantastic. But i dont race or need to replace the internal cables at the last second. That could be frustrating for sure.