WhatsApp is an extremely apt and relevant example. None of the other examples has the reach WhatsApp has: literally over 90% of the adult population in some countries — I know the Netherlands is close to this. That's huge!
A minor comment on the second rule for WhatsApp users:
> Everyone’s mobile device must run an operating system supported by said client.
This also implies that everyone must own a (not too old) smartphone running either of those two OSes, with the user having accepted a EULA for the respective app-stores. I feel strongly that the requirement of using a smartphone even when a (not too old) desktop or laptop computer is available and technically capable of performing the same client-side tasks is a significant curbing of a user's software freedom. It may warrant mentioning explicitly.
A minor comment on the second rule for WhatsApp users:
> Everyone’s mobile device must run an operating system supported by said client.
This also implies that everyone must own a (not too old) smartphone running either of those two OSes, with the user having accepted a EULA for the respective app-stores. I feel strongly that the requirement of using a smartphone even when a (not too old) desktop or laptop computer is available and technically capable of performing the same client-side tasks is a significant curbing of a user's software freedom. It may warrant mentioning explicitly.