(sorry for the late reply)
Well, there wouldn't be any real benefit from it compared to the 7.07 core. Even the changes worth porting are negligible and don't add features or were just meant for the CLI program. Sadly Matt overhauled some major portions of the code that I encapsulated in my own wrapper, so it's quite some work for little benefit. I might update libzpaq to 7.15 eventually, but we'll see.
I didn't have much time to work on the plug-in recently, but I hope this will change soon.