[krab]

> Could you split up the traffic across dozens or hundreds of IPv6 source addresses?

Yes

> I can see how this significantly increases complexity for tracking

Not really. You just track at some prefix level. In general, the ISP will hand out a /64 per consumer so that's what you can track. From there, you can build more complex and more precise grouping rules for tracking.

[bflesch]

I'd mix in some IPv4 of course, maybe pipe some of the connection via VPN interface so the physical route is not same for all packets.