Hi all again! 
I and a few others have been playing around with some concepts and ideas to make Gimel Studio a much more usable (and serious) tool for editing images. The current version has been a good experiment, but we think it can be much better with clear goals and planning.
Because of the feedback given here (special thanks to those who gave feedback!) and elsewhere, we’ve decided to take a step back and consider introducing/moving to some new concepts such as: a layer/nodes (hybrid) approach, a setup similar to parts of what @nosle had suggested (in this post), adding vector support (for design) and better file-format support.
Somewhat of a re-write and a re-thinking is currently where we’re thinking and at this point it would be great to get more people involved in the planning for giving feedback/presenting ideas to make sure we’re on the right track for providing what is needed for photography use-cases.
Both non-developers & developers are always welcome to join the project and/or give feedback, of course. 
*The goal here wouldn’t be to replace all other tools necessarily, but to be a supplement/alternative to other tools such as mypaint (as I think it could be out of scope to include a custom brush engine, except maybe implementing the libmypaint brush engine in the future…) If this sounds like too narrow of a scope, we would like to hear that too! 