[prophead]

But the onus is still on the developer to choose _what_ gets a unique URL and what does not.

It might be good for user deeplinking capabilities to change the URL every time any type of state change is made (for example sorting a list by date instead of name) - But exposing that many URLs to Google would be bad.

(This is the modern equivalent of the age-old "infinite calendar" problem that Googlebot had to deal with when dynamic calendar apps let you navigate to dates 2 millennia in the future.)

[workhere-io]

I agree with you; developers definitely have to think about the URLs they're exposing to Googlebot. But this is essentially no different from how things were before. Your example with sorting a list by date instead of name would be done with a query string (which Google does index to a point), e.g. /users?sortBy=date=&from=392. This can obviously create quite a lot of links to the same content, and developers should know how to handle this situation. Again, not different from before - single page apps don't change anything in this regard.