It also has the advantage that the page being written to, the right most leaf at the end of the index, is likely to always be available in the page cache. With random you may need to constantly go to disk to fetch the page.
In this sequential UUIDs idea, I wonder how big of a deal it is if the prefix part wraps around often? E.g. using a timestamp-based prefix with 2 bytes, if you increase the prefix every 60 seconds, the prefix will be reset every 45 days or so (60 * 1000 * 2^16) according to that README. Does it make sense to fine tune this value based on the use case or what?