Could you build it so that only the people who zapped would get access to the content?

This is what Angel Studios has done. Much of the Tuttle Twins episodes have been "payed forward" and are now available to everyone on their website, however new episodes are for members only and people can voluntarily "pay it forward". This isn't with bitcoin payments yet, as that audience grows that will likely change.

Isn't this like Vitalik's idea from a decade ago? Sounds great adapted for this tech.

You would need a guarantee that the content is useful/productive; otherwise, every person that paid could be rugged. Maybe it can work if the author of the content has a solid web of trust, I don't know