> No low latency system will be anonymous in the face of a global passive adversary.

That isn't true. The trivial system is the one where everyone has a broadcast transmitter and transmits constantly even when there isn't a real message.

The implementation of that over the internet is full mesh, which is impractical, but it's a spectrum trading off anonymity for bandwidth and there are potentially interesting points along that spectrum between Tor and full mesh, where they use more bandwidth but then a global passive adversary can't learn anything. Something like virtual circuit switching could potentially work for example.