I played on Windows. I was panicking that screenshots didn't seem to work until I found ? (which took until I referred back to your post).
Locking pitch to 180° seemed a bit frustrating when I was trying to look inside the outer icosahedron, or flip around without wiping my color buffer outside it.
I found that I couldn't morph the inner icosahedron if it was a mirror, which seemed a bit strange. I don't know if morphing it would be a good idea.
The UI was pretty obscure (not that I can complain, really). Even if you're not planning on changing it, adding directional control (e.g. 'I' to go the other way to 'P') might be nice.
I think my favourite combination was inner icosahedron interlaced with xy coordinates. xy in general was way more interesting than any of the other options, and interlaced/bend seemed like the best mirror options.
It felt like a shame you couldn't combine some of the mirror settings, like bend and interlace, but I guess those are done by two different shaders?
If you hit j then I think you have to quit? I guess that'll go when it's finished. Are you still after that information?
More shaders/shapes would be cool, but I don't have any suggestions.
Also, using a keyboard with no letters on made this a lot more fun.
As you may have guessed from the anti-social amount of screenshots I've included, I liked this quite a lot.