Collaborative databases (Wikidata, TheMovieDB, VNDB, etc.) all use serial identifiers. What is the problem with this? These websites don't want to hide how many entries they have (they tend to promote them), and it doesn't really matter if you iterate through all the numbers – the data is available through open licences anyway.

I think there are many situations where you don't want to expose predictable identifiers, but there are also examples where predictable identifiers may actually be beneficial.