Also, even if it might be possible to implement such a change, I see zero chance of it being adopted, since it would financially incentivize the privacy-eroding practice of address reuse.

Murch

No, every input needs to identify which UTXO it is spending and provide an input script, script arguments, and/or witness stack that satisfies the corresponding output script. The amount of data is the same regardless whether your UTXOs were locked to the same output script or different output scripts.