Working on the image editor is very time consuming and we have a very long todo list of other features we're keen to get started on.
We're not really aiming to replicate Photoshop in the image editor, it's really only there to help you touch up existing images and maybe do a bit of pixel art. So I think things like layers are kind of out of the question. If some of those suggestions are straightforward to add, though, I'll see if I can get them in.