I decided to draft an example of a “Trustless Oracle Contract” for historical chain IDs, which is something that could very easily be implemented, audited, and leveraged as a standard for any potential use case requiring access to historical chain IDs, without the complexity of alternative proposals.
Check it out here:
Again would like to note that assuming what the end user might want to use current chain ID for may not be known in advance, and adding a more complicated API may otherwise prevent the implementation of specific use cases that a simpler API would allow through some smart contract magic.