Fallback(secondary) bucket - if not present in bucket A check in bucket B

Has anyone considered secondary/fallback/backup bucket configuration?

Concept is very simple:
- write to one bucket read from two (if during read file not present in first bucket check for it in second bucket).

It is more complicated then "replicate" configuration (write to two, read only from one).

What is the usage of such feature?

I could it very handy while having multiple testing, staging, developing environments (even more with pipe-lines, workers etc.). Especially handy while having huge amount of files that cannot be easily copied during tests to other bucket due to limited storage or high price on such action (cloud solutions).

Is it even worth trying with current architecture of flysystem?