Haha, I instantly recognize a fan of Blender’s new design language 
This is a great concept, and I can tell you’ve put a lot of work in it!
First thing that strikes me is that I’m not a fan of the semi-transparent dockers. Trust me, I’m all for showing as much of that canvas as possible, but I’m afraid I don’t think this is the way to do it. That being said, I really like what you did with the toolbar on top (size and opacity sliders, toggle eraser mode, etc.) A barely transparent background color with the main elements being fully opaque really works for me! 
Adapting Blenders UI for switching workspaces is an interesting idea. I couldn’t tell you why, but I do like the tabs over the current drop down. Perhaps because (for me) web browsers popularized the tab as a UI element, and that each tab is a different web page. With tabs you’re not just changing the layout, you’re in a completely different section of the software. I’m not sure how Blender handles a lengthier list of custom workspaces though? With a drop down list that’s not a problem, but with tabs the solutions I can think of aren’t as straightforward.
Having tools hidden behind pop-outs… I’m a bit torn. I’ve learned to use this feature in other software and like how it helps minimize UI elements, but I do think the critique against it is valid. It isn’t very straightforward how to use and hinders discoverability. Heck, in Blender I use tools less when they’re hidden like that, and that was probably the case back when I used PS too. Something that potentially could be adapted from Blender, however, is the way the tools list are bound to the viewport. Imagine if the tools docker was bound to the side of the canvas and floating on top, and could then be toggled to be viewed/hidden with a button in the top corner of the canvas (or a keyboard shortcut). I think most of all I would love it if some UI elements didn’t have to take up the entire side of the screen, and instead was floating on top of the canvas (like you’ve done with the tools list and toolbar on top).
I can’t imagine how much work would go into a large scale UI rework like this though. 2021 fundraiser perhaps? 