Some will go Nostr-only, and yes, that is part of how it'll get traction. The dogmatic users push the unknown into the broader awareness. The "broader awareness" is the tough one though.

Looking at it like an afterthought isn't right exactly. Changes at the general level happen when a need isn't being met or when a prior way of meeting the need is inferior. That is the case here, seemingly. The rest of the obstacle is demonstrating why it's better to everyone that doesn't see why already.

Instead of as an afterthought, it's best to make it an in-addition-to approach. The existing systems are all competing with one another, Nostr isn't free from that competition. So, it should go on the list of "where to find me" with the legacy ones.

Introduction in this way is subtle, nearly frictionless and makes others ask people they trust already about it.