As an idea for unload-feature, when unloading a buffer-local minor mode
it could helpfully find buffers where the mode is enabled and disable it
before unloading.

An example foo.el mode below.  Eval the code in try-foo.el and it leaves
the buffer boldened, where disabling the mode could have undone it.

Of course foo.el can do something like the commented-out
`foo-unload-function' itself, but I think almost all minor modes would
benefit from this and that `unload-feature' might therefore handle it.

Identifying a minor mode function would be as easy as looking in
`minor-mode-list' would it?  Otherwise I expect define-minor-mode could
chuck some code in `foo-unload-hook' - if it presumes the feature symbol
will match the load filename.