I really hoped the author would discuss alternatives for distributed databases that writes in parallel. Sequential key would be atrocious in such circumstance this could kill the whole gain of distributed database as hotspots would inevitably appear.

I would like to hear from others using, for example, Google Spanner, do you have issues with UUID. I don't for now, most optimizations happen at the Controller level, data transformation can be slow due to validations. Try to keep service logic as straightforward as possible.