I've got a slightly more detailed summary at my blog:
http://models.street-artists.org/2017/12/11/inbound-qos-with-virtual-ethernet-and-policy-routing/
That thread was epic, blow by blow talking someone through setting up a QoS system for a particular wireless ISP where they had several "channels", that is, certain sources could send at high speed, and other sources only low speed.... we used two veth links each with a separate speed, it went on for like 500 messages, and used non-standard software provided by third parties, so probably not the right place to really get a summary, but here it is:
I don't know how you'd set this up in UCI, in a quick google I didn't see any UCI commands for creating veth interfaces. I think that requires the full ip package anyway as busybox doesn't do it. You probably need to have this in raw ip commands.