The network effect was what was wrong with Google Wave, which was better than email in practically every way.

If it had been possible to send a Wave to an email address (some sort of embedding?) and receive email to your Wave address, I think it would have succeeded in replacing email.

Instead, for reasons I'll never understand, Google tried to replicate the limited number of invitations system that had worked for Gmail, despite the fact that only having a limited number of people you could communicate with made the product effectively useless.

It worked for Gmail because you could send email from Gmail to anywhere, and receive it from anywhere! Missing that Wave was fundamentally different to me is one of the worst tech marketing failures I've seen.