I am not sure you are correct there kinsa?
I do prefer the idea of your pic32 external controller in many ways, but it probably adds a fair amount of extra cost (probably as much as the rpi itself). I think linuxcnc runs fairly fast and smooth direct from the GPIO pins using the dma processor, I don't really have the equipment to test it fully and the project has been shelved for the last few months as I have other stuff to do. I have been doing a little more research over the last few days as I am picking up development again and saw this thread so thought I should post a reply.
I sort of would like to combine effort as it should save both of us some time if we can get a combined distro with possibly multiple RT kernels available (I actually have a ubuntu 12 development VMWARE image with linux3.2.27 RT_PREEMPT, linux3.8.13 RT_PREEMPT, and linux 3.8.13xenomai, kernel cross compiled and they all seem to boot on the rpi though not done any latency tests)
Don't take my word for it (I am not a cnc expert and only hack on things as a spare time hobby), give the linuxcnc rpi RT_PREEMPT image a try and send some bug reports, unless other people try it and give feedback I am not going to bother fixing things. I should say I have not even tried running it multiple axis but I think someone posted a link to a youtube video of it running on the linuxcnc forum.
I am guessing that I may make some more update within a month depending upon available free time, if you check the linuxcnc forum I will probably be posting updates soon and it is the best place to send feedback on the system.
I don't want anyone to expect too much as I am terribly unreliable, and the road is paved with good intentions, but I will definitely be putting a few more hours into linuxcnc on the rpi for at least a few weeks, and at the very least should post the dma driver code.