dialog-layers seems to be breeze only, which is not very good for people not using breeze :/

Darn. Can you think of a more universal icon that has an Oxygen equivalent?

I didn't find anything back when we added this feature, worst case scenario one could copy the breeze icon into a okular- name and install it with okular but i guess it'd still look somewhat alien in other themes :/

Sadly I don't really have a better solution than the solution we did

How about format-list-ordered or format-list-unordered? Those retain at least some of the layering semantics.

Excellent idea, @rkflx. format-list-unordered is much better than what I had chosen anyway.