Hi, I am developing addon for blender VSE.
Multithreaded proxy rendering is now only feature, that is worth sharing.
When the feature is activated main blender thread will create thread running python script spawning new blender instances in background rendering each video file in project. Communication is done using sockets (port is fixed now @ 8081)
Script is using generosity of Blender, that will parse proxies at various settings even if it expects different resolution and framerate
more info on github: https://github.com/RichardAntalik/VideoTools
or demo video: