For the pans. Zig and Zag pans the initial hit into the stereo feedback delay. Set them to 0 if you want them panned centre.

The FB pan is like a width control. 100% preserves the pan fed to the FB delay (left will always pan left, right will always pan right). 0% will pan FB taps to always be centre, -100% swaps the pan on each FB loop so if a left singlan feeds the FB it will go right, left, right, left.

I could make the feedbacks as dual mono so you have a 2 time controls for it, and feedbacks. Would that solve the issue? You can’t really feed back to the reverse delay as each pass would reverse the direction so it would go backward, forward, backward, and that would get imprinted into the delay sample. It would quickly become incoherent, and would likely sound more reverb like, but would be noisy due to artefacts.

One issue is that there is a stereo mix stage before the feedback loop. I could make another version where zig and zag have an individual feedback loop before the mixer, but it would not be possible to ping pong delay taps in this case unless I add another feedback stage. Would that be desirable, given it will make the UI quite a bit more complicated?

Where would you want the filters, in the feedback loop?  What modulation, chorus/flanger/phaser, and where? In the feedback.loop, or near the mixer between delay stages are the only places that make sense, as you could add input modulation or output modulation by making a H9000 chain.

Happy to do more work in this, because it does sound pretty nice.