> I think there should also be a reasonable cap on the number of connections that can be made. Something like 300 friends sounds right. Any more than that and you're a collector, and not using the platform to foster connection.

Path[1] did that, but with a cap of 50, and then 150 (based on the Dunbar number of meaningful human connections one can retain). They had a crazy growth period but eventually went kaput.

[1] https://en.m.wikipedia.org/wiki/Path_(social_network)

I'm not sure vc funding and ads are compatible with a slow, quiet and healthy social network.