I'm flipping from securityrouter (Halon) to Vyos. Quite happy so far, except for v6 PD from Comcast.
In the attempt to 'simplify' the config, it looks like the project may have introduced some variability. In short, there is no way to include multiple interfaces in a PD statement, nor is there anyway to set the sla-len in the config language that is offered.
I tried to set two interfaces in a PD, which was bounced as invalid (although perfectly valid in the underlying WIDE-dhcp6c daemon). So, I created two PDs, each with one link. Comcast REALLY didn't do well with that (odd prefix sizes and a rapid exhaustion of my PD pool).
I also was getting /59 prefixes (which is what Comcast offers as max on a PD on business class service out of a /56 pool).
To get things working, I went down to one interface, one PD, and set a prefix request of /59, which then the vyos parser converted into an sla-len of 5 in the underlying config, which worked. It still doesn't make multiple PD internal networks work.
I went in and edited the underlying /run/dhcp6c/dhcp6c.eth0.conf file, and wrote a 'standard' dhcp6c config - one PD (length of /60), two interfaces, each with it's own SLA-ID and SLA-LEN (4) and kicked dhcp6c and everything just worked.
I would suggest adding sla-len as an option, and allowing multiple interfaces per PD statement.