Steve Shaffer:
No one is bound by the USGA/R&A Rules of Golf unless they choose to be. Since there are normally members of the AGNC on the USGA and R&A executive committees, it is highly unlikely they would ever do anything contrary to the Rules of Golf.
It is arguable that a tournament committee could proscribe a competition ball, i.e., one ball for use by all players, and be within the rules if that ball conforms to the rules. It could be a ball currently in use, or it could be larger, lighter, and/or slower. For that matter, they could mandate fewer clubs, for example, and be within the rules.
The complication is not the USGA /R&A rules, but the players and the equipment companies they represent. What would happen if they started a tournament, and nobody came?