I think you make some good points. I have a few comments:

-Bitcoiners are kind of a seed for content here, but I agree with you that it's a lot. That's part of the reason I post random shit about Egypt and other random stuff over the past year and a half. A new social ecosystem requires some diehard people, but also needs certain roots for broader involvement.

-The inability to delete is a feature, not a bug. Once you sign a note, it's out in distributed relays. However, incentive-wise, I think high-accessible perpetual notes will rely on some form of economics or payment. Over the long term of time it will likely be unseen or outright deleted if a small account posts something they don't particularly endorse anymore.

-I think zaps will be an onboarding tool for bitcoin. Existing bitcoiners will be like "yeah I know what those are" but new coiners will be like, "wait what are these?" and it'll be a learning experience. It's a friction point, but potentially a good one. Also, some Lightning/Ecash wallets can be dollar-denominated.

-I think key management is probably the hardest long-term part. Even for power-users let alone newbies. Because with power-users we might understand it better, but also our stakes for fucking it up are higher.