Can recommend a P4Win-like alternative for Perforce, hopefully that supports shelving and may be open source? Needn't be cross platform, just Windows would be fine.
I'm asking as I'm not a fan of the new P4V interface, and I found P4Win a lot more intuitive, easier to use, and much more stream lined.
I haven't found much in my Google searching, but I'm hoping this nexus of programmers might know of a hidden jewel out there. :)
This isn't really an answer, but I don't have enough rep to comment on the original post. If your primary concern is support for shelving, you can still use shelve/unshelve through the command line. You could probably even hook it into to P4Win UI using a simple Python (or your language of choice) script that's set up as an external tool that runs on changelists.