It is entirely viable to never have more than 1 or 2 open pull requests on any particular code repository, and to use continuous delivery practices to keep deploying small changes to production 1 at a time.
That's exactly how I've worked for the past decade or so.
This is especially useful when you're using them for customer or user IDs - being able to easily spot your important or troublesome customers in logs is very helpful
Personally I'd go with a ULID-like scheme similar to the one in the OP - but I'd aim to use the smallest number of bits I could get away with, and pick a compact encoding scheme