There is a distinct lack of decent identity management/security in all of the version control systems I've used. It's a hard problem to solve, especially in a distributed/decentralized system (like git). Signing git-style commits is problematic in the face of merge conflicts or rebasing. A patch-style system (like Pijul) probably makes this easier: if everything is a patch, every patch can be signed atomically.

I'd really like to see a DCVS with better signing support and with some form of access control (on the remote), so every change can be traced back to the author, and so that some parts of a repo can only be modified by specific authors. Git hooks (on the remote) can sort of achieve the latter, but it's a bit of a pain.