Yes sorry I should have been clearer, it’s the connections from clients having to timeout and re-establish upon IP change that is the issue. Specifically where those packets might be going over a SD-WAN type solution where a WAN change is non-disruptive to SD-WAN destine traffic. It relies on clients having NAT addresses and using those addresses for Internet destination addresses (not just private space).

Another issue with SLAAC/lack of NAT on the LAN clients is you can’t do policy based routing on the router, eg I’ve got a fast fibre but it’s costly to use, I’ve also got a cheap and cheerful cable/DSL line that I use for backups and FTP. I want to route all requests to my backup service (which has a domain that resolves to a public IPv6 address) via the cable/DSL and everything else via Fibre. Easy to do on IPv4.

But, nothing you said is inherent to NAT, you should read up a bit more on iBPF for the latter and the former works exactly the same way on v6 as v4. Static routing is not really a thing unless you’re a really bad network admin- for sure your ISP wont be doing static routing to your home.

Can you talk about this some more? Also do you mean eBPF or iBPF or iBGP? If it's BGP that's just too complicated/expensive for a lot of the small businesses I deal with.

Policy routing works exactly the same on IPv6 as on IPv4. People misusing NAT or internal addresses to handle policy routing are the problem.

I've no idea why SLAAC would prevent you from doing policy routing - the prefix is deterministic.

In IPv4 I presume you guessed who each host is by some sort of DHCP registration. For IPv6 you would use either NDP, or perhaps even way more secure SEND enhancement with PKI instead. Of course static assignment still just works, including in NDP/SEND. (e.g. by MAC address or per link)

RIPng/OSPFv3/IS-IS/EIGRP can also tell other hosts which route you prefer packets to return by with better granularity and dynamically. This works even better with v6 since global addresses are always available.

The above doesn’t work if you are dealing with client devices that don’t support routing protocols (Ie phones, laptops, tablets, CCTV systems, PCs etc - everything except routers and servers) and especially with BYOD devices.

Also perhaps I missed something in your reply, but policy based routing - the definition I have of it - encompasses more than routing different subnets via different WANs. Ie routing based on destination port, IP DSCP flags, WAN utilisation etc rather than just by source.

And as I’ve mentioned elsewhere, the cost and complexity of running routing protocols is a non-starter for many small and/or low margin businesses. Think retail or fast food or fuel etc.