I'm in the middle of implementing SSH agent support for svn4idea and git4idea; this effectively allows single sign-on for all SSH-based services, with the option to delegate authentication to smart cards or similar hardened tokens [including over a network, without exposing private key material]. One big issue: The CVS plugin for IDEA uses a patched version of trilead-ssh2 which adds support for using SSH over or HTTP tunnels. Unfortunately, that patched version is several years out-of-date, while the fork of Trilead SSH2 actively maintained by the folks at TMateSoft is both API and ABI incompatible.
Trying to keep multiple JAR versions in the classpath, which IDEA appears to have been doing, falls down when moving to current trunk (where SSH agent support has been submitted, and has potential to be merged) due to the aforementioned ABI incompatibilities. Porting the patches used by the CVS plugin to a modern release seems like a waste of time for something that's only relevant in a very small number of scenarios, for a version control system which is only rarely used any longer anyhow. One could rename the old version to avoid namespace clashes -- this is perhaps the easiest approach if we want to retain functionality (and don't want to add agent-based authentication to the CVS plugin), but that means that the CVS plugin doesn't take any advantage of new performance/security/bugfixing work.
Notably, none of the other version control plugins IDEA bundles appear to have explicit functionality running over SSH over proxies -- this is entirely specific to CVS. I'd expect that if it were a feature that folks used or cared about much, it would have been ported to the newer SCMs. On the other hand, withdrawing functionality that users somewhere may be depending on is unfortunate, even when said withdrawal enables new functionality likely to be of more use to a larger audience.
Thoughts? I'm not really clear on where I should be asking this question; it doesn't seem like a good fit for a users forum, but I don't see anything that's obviously the right place to ask questions about product direction.