The slow-loading Matroska bug has been fixed by the incredible developers on the ffmpeg team (see the link in the post above for ticket details). This fix changes the entire discussion. MKV would now be the recommended export preset and Edit Friendly format for all lossless codecs like HuffYUV and Ut Video in order to preserve all color metadata. This would require the next release of ffmpeg to be bundled with Shotcut in order to work, of course.
I realize I’m not a developer and I’m in no position to call any plays. I’m just raising awareness to what is possible now that ffmpeg is working as expected.
EDIT: I reviewed the thread from the top and realized D_S should be added to the at-list as well.