I think that could be very beneficial. If it were a built in feature for HTTP (or more broadly level, maybe TCP/IP), it would not only save people the hassle of reinventing the wheel, it would also be easier to ensure it's on by default for all static resources and thus get benefit across the board.

Perhaps it could be done in a flexible, extensible way as well. Create a limited language (no loops or dangerous stuff) to express policy, search order, etc. And design it so the client side doesn't necessarily have carte blanche and the server side can maintain some control if necessary.