I've got a similar issue to this one, but has progressed to worse.
I've tried removing two broken eyeball fittings and both easily crumbled.
I tried using one of the crappy plastic fitting removal tools to get out the rest, but it appears that some genius cemented the threads. I tried to chisel one out and I can't seem to do it as it just comes apart in small pieces and I'm at the point where there's nothing left to catch the chisel on...

I see on another return jet that it looks like someone else had a similar problem and there has been some retrofitting. There is PVC fitting extension that comes out away from the wall and looks like there might be a metal threaded pipe between the extension and the PVC pipe in the wall. Does anyone have details on how to do something like this? A YouTube video would be great, but I can't seen to find what I'm looking for.