In the fine print, only to be used against bad actors (w/guarantee that filenames under x chars would never be charged), or that too problematic? building good faith into policy + "hiding" info...

Reason - to not overcomplicate or give appearance of nickel-and-diming

No, just charge for the amount of storage they use on your server. Not the amount of data you think you’re storing. In non-special cases these will be the same number.

Makes sense.

Would there be any engineering/management pushback on the customer side? "we have to write a tiny script", "this is non-standard" / "why are you the only ones who charge us for filenames?"

(have limited knowledge here)

Not sufficient, unfortunately. The strings for file paths are stored in wholly different infrastructure with wholly different optimizations. It probably lives in your database. You really don't want people just stuffing gigabytes into that, payment or no payment. Odds are you didn't plan your control plane around, "what if someone uses our strings as encoded data?"

They won't do it if it's not free