We should not forget the essentials - low latency and sufficient throughput for implementing more demanding communication modes such as audio and video.
Often these essentials are at odds with the rest of the requirements. For example, the lowest possible latency will be achieved with a P2P architecture similar to WebRTC, but this partially reveals your location to the other party due to the known IP address. The ISPs also get to see how is talking to who, which is undesirable. The solution may involve using Whisper, onion routing, creating fake random traffic or other measures that have various trade-offs. We need to think how many of these technical details are reasonable to expose as configuration options for our users.
Perfect Forward Secrecy seems pretty straight-forward compared to these other concerns.