So when you just want to edit the patch before the commit, you can do so
already, for example using 'M-k' (diff-hunk-kill) - or just 'k' if the buffer
is read-only.
But of course if the idea is to really "discard" some changes, that works.
Yeah, this is about really discarding the changes.
It's like using C-x v D as a kind of review view. You use it for
committing what you want to keep and getting rid of temporary changes
you made just for development purposes, such as additional debug prints.
When I used Magit I used its magit-discard for this a lot (the docstring
for that function talks about conflicts but it's also useful without those).
One question I have is whether this should offer a y/n prompt to confirm
discarding the change. Do you have an opinion on that?