I know how Google infrastructure worked up to a couple of years ago, including user-specific storage. What you describe would be a very large undertaking across a large number of projects. Due to legal restrictions, Maps has something ad-hoc just for South Korean tiles, which is a much simpler problem. Not only it's extremely clumsy, it also adds a lot of limitations:

https://stackoverflow.com/questions/31568460/google-maps-sty...

https://www.theverge.com/tech/2013/10/13/4835026/why-google-...