And that is perfectly fine. Your mock up looks really good. I do not intend to demotivate you or put down your efforts. I also understand not everyone can code and it can be hard for non programmer to contribute. Even I am not a programmer and I can not code.
But it is a fact that your mockup, even if it is beautiful, it is a complete redesign of the interface and it was done without any discussion with the devs as far as I know. Since you are not a programmer you might also not know what is possible and what is not with the technology that krita uses for the UI. You might also not know the time it would require to do the complete overhaul as shown in your mock. To make your mockup a reality we would need a volunteer programmer or help from the main devs who may have other priorities.
Again I am not discouraging your efforts, I would advice you try to help in designing smaller things first and not propose complete redesign. I would advice you to help us in UI like the recent Bundle creator thread or other part of Krita. But this is a just an advice from a non dev user not krita official dev, so take it with a pinch of salt.
That is an assumption on your part, I won’t take it as a true fact. I have seen many artists contribute to krita and I know that the Krita devs do paint.
Your expectation of what the UI should look, for it to look like designed by artists may be something else. And my expectation may be something else. I may find your redesigned mock up really alien and breaking my work-flow even though it looks slick, it may have some issue with the placement of buttons etc we would never know unless we use it. it is subjective. Hence it is important to discuss and then contribute.
Hope you will continue to help us, there are many challenges here in the forum. The devs ask users about the UI you can chime in. I already linked a thread above.