My current solution for this has been to use ten brushes to bind my eraser of choice to ‘e’, and then put the transparency painting mode on ‘c’ (like how CSP does it and because it’s conveniently next to the swap foreground/background color on ‘x’).
This is also an idea from CSP, which allows you to make any number of tool preset categories, put anything in them, and bind them to any key, but I think an ideal solution would be allowing the hotkeying of brush groups, grouped by tagging. Each group would remember the last selected brush within it (again, similar to CSP).
IDK how feasible this is, especially because hotkeying brushes at all currently relies on a plugin, but it would allow you to have a tagged group just for erasers, or even multiple groups for different use cases (hard vs soft erasers, etc.).
I know I’ve historically gotten a very bad reaction when I suggest “lifting” features from other software, but the modularity of this approach solves this problem, and is extremely useful to workflow with all other brushes as well.