Interest rate swaps, credit, loans, fixed income, exotic derivatives, CDO, whatever.
You have to hedge the interest rate risk somewhere or get stuck with huge collateral requirements/XVA.
Cryptocurrencies don't solve the problem since they're largely traded on opaque exchanges and other l2 solutions even less trustworthy than the libor cartel.
While there are rumors of wash tradings on some exchanges, the price at which such trades would be going will be constrained by the larger network, and the risk of triangular trade will limit the possible divergences to a larger spread (instead of going one direction only)
Add enough data, and you may get something that would be almost impossible to trick, simply due to the sheer number of exchanges, and bots that would gladly take the money of those who would try to rig the game.
Maybe the big players could agree to record a decent portion of the transactions transparently across a clearinghouse or blockchain that would be audited manually or cryptographically. Then you have real-time approximation of rates.