There are currently a few major potential improvements to be made to the actual encoding performance. Some in task distribution, others in optimal resource utilisation.

Let's see how closely we can match Resolve's own DNxHD encoding performance.
Some considerations will have to be made to optimize for a spectrum of popular proxy codecs. Casting a wide net, let's aim for DNxHD/HR, ProRes and Cineform.

H.264 and H.265 are off the table for now as inter-frame codecs because of drastically different multi-threading implementation (namely in incorporating chunked-encoding)