I've been happily using the curl backend for a bit now and it seems to work fine, so I'd like to get this polished and committed.
Since the curl backend works, then even if the wget and powershell backends aren't fully tested, the workaround can just be to tell users to install curl and make sure it is in their path (or to pass the insecure-http option that falls back to the existing implementation).
So perhaps we can just patch cabal to warn on using wget or powershell backends that if there are issues they should try one of the fully finished options, and then we can merge?
Alternately, someone can jump in and try to give a hand with the other two backends -- they're very close.
-g