Hold an event to encourage players to use the New Arena System. Get people familiar with the system so its used more often. This will also help GMs finish the testing phase.
Give players rewards if their team completed their 10 matches for the week.
Things that GMs will have to do for this event --
Announce that the event is happening.
Help players that don't understand the system.
Be reachable in-game to answer any questions. (This can be for a period of time during the day, for a couple days during the week)