HTTP is inherently stateless. I think it was probably a mistake to not more clearly change this with the move to encrypted transport - or rather, I guess web sockets are a better evolution of http/1.1 than just wrapping http/1.1 in tls.

Without state there isn't any great way to do transactional changes, without some added state; if you say get me a list of users, then update user x, y and z; there's no way to make sure you're not working on stale data.

You could run the logic on the server (send js to execute in a transaction), or you could have protocol level support (like with sql: begin...commit/rollback).

But rest/http will always be a document store, and it will always be challenging to maintain data integrity accross documents/resources. It's not what it was designed for.