We were well aware of the contents of rustc-serialize when deprecating it. I wrote the majority of the base64 and hex modules!
The entire point of open source development (IMO) is that it empowers people to Make A Thing when they see a need. Does rustc-serialize provide something that doesn’t exist elsewhere and you don’t want to continue depending on an unmaintained crate? Copy the code out, follow the terms of the license, and publish it! You don’t need the permission of me or anyone else to do that.