I'm not sure you gain much by moving the forward secrecy to a weekly or session based level, and I think you lose a lot in terms of simplicity. It is simpler t

I'm not sure you gain much by moving the forward secrecy to a weekly or session based level, and I think you lose a lot in terms of simplicity. It is simpler to design and analyze if it applies at every message. It's a design for the best case. No longer need to make judgement calls on if 1 week is enough, or maybe 2, or maybe some middle ground.