Just know I had a use case where I wanted to revert some code, but the 
hunk I was presented with contained stuff that I didn't want to revert. 
So I pressed 'e' and was told that that was an invalid response. I'd 
like to be able to edit hunks when doing revert.

A workaround would be to first record and edit the hunk to only record 
the stuff I want to keep, followed by a revert.

However, in my case I'm not really ready to record the non-reverted code 
so I'd have to unrecord after doing the revert. That seems a bit 
excessive.

Agreed! Please help us test the feature (already in darcs darcs).

darcs get --lazy http://darcs.net/reviewed darcs

We may need to tune the UI so it's more obvious how to make it work

Oh hang on, I think this is even in the current beta

yep, cabal install darcs-beta and give it a go. The help text may well 
need some work, so do let us know how you find it.

Fantastic! Great to see my wish already fulfilled even before I needed 
it. :-)

However, I seems rather buggy. I never managed to get it to work the way 
I wanted. I'll file another ticket for that.