It would be useful to have a selection brush where you use a brush to create a selection. I am always using the selection outline tool but I often have to redo the selection multiple times because it added some small part that I did not want. With a brush it would be much easier to add/remove selection parts and the selections would also be smoother compared to the outline tool.
That is already possible. See the manual: https://docs.krita.org/en/user_manual/selections.html#global-selection-mask-painting-a-selection
I looks like it is possible but the workflow of it seems really bad, at least for me. When I want to select something I will have to go to the correct layer. And when I want to adjust it with the brush I have to again change to another layer to change it. Then go back to the previous layer. Depending on how fast I can find the layer again, it could considerably slow me down. I know it is not that easy to just add a tool. This bug can just stay closed but just something to consider maybe for future tools like this.