I would expect this system to ultimately be used under a commercial HF license rather than an amateur license, given the feature set and that it seems to have much more in common with military systems like ALE than amateur practice. That said, because of the scarce supply of HF bandwidth, commercial HF licenses are quite restrictive in the US. For the most part, you are only allowed to apply for one if you are an infrastructure operator that needs a contingency communications capability for disaster response. That said, the FCC has permitted experimental licenses for some commercial applications like high frequency trading, so perhaps the situation will become less restrictive over time.

That said, commercial licenses are not per-operator like amateur licenses, so you would potentially only need one to cover the entire network. Some of this is ultimately negotiated.

Correct. Encryption (or more specifically, obscuring the meaning of a message) is generally not allowed for amateur radio stations except in very narrow circumstances. So any hams using this would have to turn the encryption off.

However, it looks like this stack has encryption available as an option for stations who are transmitting sensitive data and are NOT operating under an amateur license. (Probably government-sanctioned communications or emergency humanitarian efforts.)

Going to be super pedantic here - in ham radio you don't broadcast, you transmit.

https://n5dux.com/ham/files/pdf/Data%20Encryption%20is%20Leg...