mmm… not sure how that would work.
To make a concrete case: imagine a feature that let you designate a second account as backup for a primary account and a timeout after which the second account can be used to recover the primary account. You need to be able to extend the timeout periodically before expiration and if you fail to do so (e.g., you have lost the primary key), you can then use the backup key.
One way to implement this is to create a delegated signature signed by the primary key that rekeys the account to the secondary key if the timeout is expired. The timeout has to be stored in a smart contract where it can be extended and the smart signature has to check it is part of a group transaction involving the smart contract for approval.
This could work but it is complicated by the fact that you need to store the delegated signature, if you lose it you are out of luck. If a smart contract could be part of a multisig then it could be used to rekey the address directly.
Another alternative would be if smart contracts could store transactions in their state and then send them to the blockchain at a later stage. So you could send the delegated signature to the smart contract and have it issue it to the blockchain if the timeout expires.