If I understood correctly, in order to properly enable a eth1 <> eth2 bridge, you need both a way to introspect and validate state on both eth1 and eth2?
Yep!
If so, is there a way to possibly generalize this for say any EVM-based blockchain?
It would be a blockchain-wide feature to have introspection capacity for specific other blockchains, and this would need to be implemented on both sides at protocol level, so I don’t expect this to be the mechanism by which ethereum becomes some kind of cross-chain interop chain. For that, you probably want the light client approach.