I know this is a very broad and ill-defined question (I'm just starting to understand the datomic model,) but I'm trying to get a very back-of-the-envelope idea of what "datomic doesn't have arbitrary write-scalability" means in practice.

I guess I'm curious, on an order of magnitude level, about what scenarios datomic can support, and where you would hit a wall with datomic even if you were willing to throw a lot of machine at it.