Couple of features I've been finding myself wanting to have:
Ability to save a set of layer operations as a template that you can import into projects. Currently, if I want to use a set of transforms again to create another piece, I have to use another piece as base and delete other layer operations that I do not desire. If I'm not also careful I might save over the original piece :(
I would also want to be able to parametrize my layer operations. What I mean by this is for example let's say I have layer which is taken as a input to two transform layers which offset the layer position by 100 pixels, the x and y coordinates respectively. However, I might later decide I would want to change this 100 to 1000 later. It would be easiest if there was some kind of common variable which could be used to parametrize these transforms.
Another idea would be the ability to repeat a transformation with changes. Say I would want to repeat my drawing N times to the left with a offset of X pixels. This gets quite unwieldy to manage with high values of N and changing the offset X would be horrible :(.
One method of solving this could be allowing layers to feedback into a layer stack and limiting the amount of feedback loops.