I don’t like the idea of permissioning, especially since the main point of contracts is to allow untrusted people to deploy untrusted code. But I understand the desire to have contracts that can interact with assets on AH.
Whether some of AH’s blockspace is available for contract execution is more a matter of whether that interaction must be synchronous or not. For interactions that don’t require synchronicity, it’d make much more sense to deploy those contracts on a smart contract system chain, rather than just adding another thing to AH. If contracts do require synchronicity, then the smart contract chain could also have an interface to accept/represent assets from AH. Then instead of a slice of blockspace, the whole block is dedicated to contracts.
For interactions that absolutely must be synchronous and must be on AH, then we could explore the idea of hybrid blockspace where we set aside say 10% of the blockspace for contract execution. If there is a lot of demand for this tranche of blockspace, then the gas price will increase a lot, motivating contract developers to migrate to a contract chain or rethink their application architecture to work asynchronously.