I disagree. Deduplicating filesystems often depend on hash equivalency meaning data equivalency. They may or may not have modes to validate all data before deduplication, but these suck for performance and are often turned off.
E.g. I make two things that hash to the same thing. One is a contract where I'm obligated to pay back a loan. Another is some meaningless document. I give them to a counterparty who puts them in their filesystem, which later scrubs and deduplicates data. Since they hash the same, the filesystem removes the contract and leaves my meaningless document (or never bothers to store the contract because it already exists, if deduping online, etc).
Note that this is a chosen prefix collision, which is much more demanding (and more useful!) than finding a collision in general. And this leaves aside that SHA1 is looking increasingly vulnerable to preimage attacks which further broaden the attack scenarios.
