dave taht here (project lead for cerowrt)
doesn't have the ipv6 issues you mention, so far as I know. runs all forms of ipv6. bloatlab #1 has been dual stack for over a year. Cerowrt Only runs on a few pieces of hardware, tho.
Way more details on the web site and cerowrt-devel mailing list a better way to ask questions.
I'm kind of sad that you got no replies here, I thought everybody had heard of bufferbloat and codel... and cerowrt by now