@jan_berg This approach seemed to be working for me: https://wiki.cable-wiki.xyz/OPNsense
Caveats:Can't be done through UI, needs to be executed in a shell. The tunnel will not be visible in the UI. Doesn't persist. Would need to re-execute every time the WAN comes up and has a global IPv6 assigned. Need to extract the AFTR name and its IPv6 address. In my case, the name comes through via DHCPv6 from the ISP as option 64. Could extract it via tcpdump. Then resolved it to an IP address and used that when setting up the tunnel. Breaks again if AFTR name/IP changes.
So, no real DS-Lite support in pfSense currently, but possible to set up manually.