No, as I said, this doesn't help. You would need to sign the most popular gems and all their dependencies and the dependencies dependencies. Given that a pretty much standard rails app can easily pull in hundred or more gems that's quite a bit of work. It's doable, but I only see that coming if for example rubygems requires a key and gem signatures.

Then there's still the unsolved problem of providing key trust - the current implementation relies on self-signed certificates.