Legally what would happen is any time another state moves in front of Iowa the date for the Iowa caucuses would move up. The power is actually the other way around the DNC has to get Iowa to give up and revoke/ignore the law in their own state to put another state in front of/with Iowa. Any state can move their own date around the best the DNC can do is maybe refuse to acknowledge delegates from states that skip the line but that's a very big button to press.