How about for first 2 weeks you only enable 3v3 arena?
People are discouraged to play 3s for few reasons.
My point of view tells me that it's easier to find 1 player and queue instead of 2 players.
Following that, 2s queues are faster. You queue up, mostly you enter arena in less than 20 seconds. 3s? Let's queue up and wait ~5 - 10 - 15 minutes and spam global until someone else queue.
My main focus would be to get more casuals trying to gear up or just play 10 games for points to queue 3s. No one likes to get farmed by smourne Thundercleave or LSP teams pushing for R1.
We need more equally geared and skilled teams queuing into each other.
As someone suggested before, lower requirements to buy shoulders. 1800 should be sufficient. Also you can slightly award 3s with more arena points than usual. 10 games below 1500 award let's say 400 arena points, make it 600.
Use Cataclysm mmr system in 3s. It takes way too many games to get 1000 rating.
Make in game announcements. Below login message, put something like We have increased 3v3 arena awards, queue and get more points.
Introduce more titles, idk whose idea was this bull**** with Gladiator and Rival only. Make it 1800+ Challenger, 2000+Rival, 2100+ Duelist, top 3 Gladiator, R1.
I think 2 weeks is not long period of time to disable 2s queue and test this out. Worst thing what can happen is few angry players raging on forums.