There is/was discussion in the standards body of using the SRI hash for exactly this purpose. It sounds really promising but iirc there was a privacy kink to work out.
Person goes to a porn site, get's file #A.
Spying site, offers file #A, but never delivers it.
If a person already has #A (i.e. doesn't request it), spy site knows they've been to porn site.
As a bonus, developers could use it knowing that there is much less likely to be a performance hit from fetching it.