Just had an idea that an an "inverse timelock" can be made
almost-certainly automatic: a revocation UTXO shall become
anyone-can-spend after a timeout, and bear some non-dust amount.

Before the timelock expiration, it shall be spendable only along with
the covenant-locked 'main' UTXO (via a signature or mutual covenant)

This way, after a timeout expires, a multitude of entities will be
incentivized to spend this UTXO, because this would be free money for
them. It will probably be spend by a miner, as they can always replace
the spending transaction with their own and claim the amount.

After the revocation UTXO is spent, the covenant path that commits to
having it in the inputs will be unspendable, and this would effectively
constitute an "inverse timelock".