Datomic is really neat but, for any system that operates at significant scale, I think the approximately-10-billion-datom capacity is probably too great a concern.
For example: Stop&Shop has 415 stores, and
365 days * 415 stores * 100 purchases per day * 50 datoms per purchase
will fill up your system in 14 years without even spending datoms on inventory and the like. And that "100 purchases per day" could be low by a factor of 5 or 10 (I don't know).
Datomic shards naturally though – Datomic queries are functions that take database values as input. You can pass multiple database values as input and join across them. This is a first-class construct. I don't remember if this works in Cloud but it definitely works in onprem.
For example: Stop&Shop has 415 stores, and
will fill up your system in 14 years without even spending datoms on inventory and the like. And that "100 purchases per day" could be low by a factor of 5 or 10 (I don't know).