Baking this requirement into law is something that should ONLY be done with the utmost care and clarity.
For example, does "federate" mean that large servers must actually connect to a significant portion of the external market of users or just be open to it? How does the legal requirement overlap with local moderation choices? Are there exceptions for instances where the rest of the market chooses to NOT federate with them (e.g. Truth Social)?
"By law" sounds nice, but "Buyer beware" too!