If you have insert, update, and delete then you can build any other operation from those primitives as long as you have the ability to batch a composite operation. So there's no need to extend the OT algorithm to support other kinds of primitive operation. For nested structures, addressing via ids or linear addresses has to be taken into account but that doesn't affect the OT transforms, it's one layer above. So it's possible (though not easy) to have an extensible OT system without exponential complexity.

Still, avoiding OT has led to some interesting new ideas and I look forward to seeing how things progress.