Sounds like a great use case.

I’m assuming your nearline drives speak SAS? Are you doing redundant controllers on the backplane for multipathing and for fault tolerance? I’m not sure if bcachefs specifically supports it (or if that would happen at a different layer) but distros in general should support it.

TCO gets split into CAPEX and OPEX, so you come out ahead on the initial purchase even though it uses more power in the long run, which surely looks better to the business.