Except IPv6; the rationale fear of the tracking involved created the pressure which begat IPv6 privacy extensions...
Nope ATM my ISP uses dual-stack with public IPv4 and IPv6 prefix, nice actually. Unlike the incumbent they have no publically known upgrade path into the future (but they are owned by Spain's incumbent so probbly have something in the works as well). Telekom is in the process of switchin their mobile network to IPv6 and 464XLAT. I would not be amazed if they would switch to that for their fixed line business (even though they championed the IMHO sane ds-lite extension lw4over6), but they also sit on a big stack of public IP-v4 space so will have time to wait for more traffic to switch to IPv6 before relegating IPv4 from native to as-service-over-IPv6. I would guess Telefonica will behave similarly (except their pile of IPv4 addresses used in Germany is considerably smaller, so they might have to move earlier).
6rd is just that, except that the ipv6 prefix is determined by shoving the ipv4 onto the end of some initial prefix, so they change in lock step. ATT was doing that when I first signed on, but these days they're doing full ipv6 native prefix.
BTW I ran IPv6 only on my lan for a full year, using NAT64, DNS64, an http proxy, and Tayga. The things that didn't work were a small number of computer games. Minecraft at the time for example had only partial support (these days I think it works fine with ipv6 ... mostly).
I'm convinced if we passed a law saying any consumer ISP which offers 100% IPv6 only with a /56 by default and /48 for anyone who requests it, by Dec 31 2022 would get paid $200 per customer signed up and connected... the switch would happen without incident.
It's surprisingly hard. You need to send packets and control the receiving end so you can check. But also there are multiple hops. Anyone in between could alter DSCP. The norm is that it doesn't survive end to end. In fact DSCP is not designed as end to end. It's designed as end to end within a single domain. Where a domain is something like a single ISP or a single business campus or a single university, or your wired LAN in your house.
When you capture on an interface anything recieved on that interface has not been processed by iptables yet. But things sent on the interface have been all the way through. So what you see is no tags on packets coming in and tags on packets going out. But if you capture on the "other side" of your router you will see the opposite