VSE Alternate thread proxy building / Improved proxy building performance

Essentially, while building proxies in blender's VSE, the video editor is pretty much unusable as it's so laggy.

Would there be a way to improve this so that you can still edit other clips while the proxies are building? The preview lags so much, even on 25% render size. Keep in mind I'm trying to edit other clip's that I've already built proxies for, clips that usually wouldn't lag on 25%. Maybe FFMPEG could even be used in the background to render lower quality versions of the video using the GPU? It doesn't seem that the GPU is being used at all in proxy rendering or blender VSE rendering at all.

The point of this feature request is to make workflow in the VSE much better as there wouldn't be as much dead time waiting for proxies to render and not being able to edit.