On a second thought, this criteria is not good. Technically it should be possible to send a tx with any amount of outputs. And if people started feeling generous and started giving bitcoin to every existing wallet, the UTXO set will explode but that would be part of the protocol. Maybe another technical solution can be implemented to ease RAM requirements because of the UTXO set. Maybe in the future SSD storage will be fast enough to store everything. Only 87 M UTXOs now. Nodes should be able to handle 9 B UTXOs if btc was to be truly global.