This won't be a detailed answer but a principle: have as much control over each user as you like up to a certain scale followed by gradually decreasing per-user

This won't be a detailed answer but a principle: have as much control over each user as you like up to a certain scale followed by gradually decreasing per-user control if you keep gaining users. The company can choose whether to stay smaller and keep full control over all users or, say, federate their protocol to allow other providers to freely join the network-effects-dominated system, so users could decide for themselves which other users to subscribe to. The original company could then retain full control over their size-limited portion of the users, those still wanting "full service", by offering such benefits as "safety" from bad opinions as an incentive. This would certainly apply to cases such as Amazon, where the bigger they got, the more helpful they would have to be to small competitors instead of putting them out of business.