“Eraser mode” can be achieved through a blending mode. The smudge brushes are quite different. And now they support different attributes, such as “mask brush” cannot be used in smudge engine. So this is a very big problem.
Are you saying “ Fill gaps in Fill Tool - Develop / Feature Requests - Krita Artists (krita-artists.org)”？
Now it is in @Deif_Lou’s todo list. Let us wait for his good news.
Dragging colors directly from the color wheel seems unlikely. A previous post was discussing adding foreground/background color components to the color wheel. If it succeeds, dragging may not be difficult.
I have thought about something similar, even including processing multiple pictures at once. In this way, we can analyze the color style of one artist at a time and divide it into different swatch groups of a color palette.