Hmmm, I don't think converting a 500k codebase in C to C++ has a meaningful cost/benefit ratio, especially for security critical code like this. It might be justified to do in something like Rust, but at that point I think it's better to move on from GPG entirely. The OpenPGP standard itself is showing its age (eg. no perfect forward secrecy) and is extremely complicated. I think GPG should be left as-is, and the community gradually move to something simpler, like OpenBSD's signify[0].