ok except "full planet datasets" make little sense for terrestrial features. Splitting .. aka sharding the files into basic continents would make SO much sense. Asia is big, but no requests for Africa mixed in.. Australia would be manageable?
The main reason PMTiles is one file and not two or more files is that it enables atomic updates in-place (which every mature storage platform supports) as well as ETag content change detection in downstream caches. All of the server and serverless implementations at http://github.com/protomaps support this now for AWS, S3-compatible storage, Google Cloud, and Azure.
Also, I'm pretty sure range requests are going to be difficult to cache. That implies going to origin every request which is bad.