> N+1Sec is a similar protocol [to multi-party OTR, which requires participants to be online at all times to renegotiate keying material] with some improvements. Note that these protocols have a lot of algorithmic complexity and tend to scale badly, especially when you add latency into the mix.
It's unclear to me, though I can hardly imagine it being the case, whether this protocol requires all participants to be online at all times. The quoted answer surely sounds like it has that drawback, which is why I never really considered it as an option (leaving the Signal Protocol with "server-side fan-out" as the only good option).
If it does not have that drawback, having another protocol is a great thing, assuming what Wire says is true regarding OpenWhisperSystems trying to get millions from them for implementing a supposedly open source protocol.[2]
[1] https://security.stackexchange.com/a/127331/10863
[2] https://medium.com/@wireapp/axolotl-and-proteus-788519b186a7