BIP 110 is the most neutral rule that it can exist. It removes all large arbitrary data. By this it achieves the goal to allow only monetary data and lets say a negligible amount for non-monetary data that can be used sensibly and that can't abuse Bitcoin.

GitHub

bips/bip-0110.mediawiki at master · bitcoin/bips

Bitcoin Improvement Proposals. Contribute to bitcoin/bips development by creating an account on GitHub.