I'd say verifiable app logic security. Formal verification (e.g. Certora, KEVM, SMTChecker) is part of it, but then you have fuzzing (foundry, echidna, ...), crypto-economic soundness, and simulations (e.g. modeling with @gauntletnetwork (closed-source) / @PrimitiveFi's Arbiter - github.com/primitivefinance/…), robust unit testing (foundry), better static analysis auditing tools (slither, pyrometer - TBA soon, ...). Hopefully, something that'd make this entire process straightforward for most devs to be able to give high security assurances about the code they write is secure without having a huge barrier to entry for production code (spending hundreds of thousands on audits or senior devs that know this stuff - very scarce resources to come by).