From oleg comment:

"So, yes, i think best thing to enable all the features that shotcut using from mlt is to have video-editing mix-in, where ffmpeg and mlt have uses enabled,"

BUT INSTEAD...

Instead we should augment the existing "mediaformat-video-extra" (and maybe "mediaformat-video-common" to some extent) to enable all these things. This is what these existing mix-ins are for. So ffmpg and mlt should have basically everything enabled via these mix-ins.