First of all, transmog system is pretty good. It offers opportunity to trade with other players, gain honor, even transfer honor between characters by buying cases from them. What I don't like about it is the mechanics surrounding the arena transmog.
What's the point of having a rating requirement on an item if it can drop to anyone lucky enough from a case? Where is the prestige in having 2450 transmogs when every second 1350 player is running around with them. Arena transmog should serve to motivate players to push their rating beyond 2050. It's pretty inactive above 2200 in soloq and this would help.
Speaking of 2200 rating, my suggestion is to make the heroic weapons and pve shoulders available from soloq, there is no point in queuing 3s, because nobody except for wintraders plays them anymore. And reaching 2200 only to find out you can't buy anything for that rating is a big disappointment.
Another suggestion to make 3s more active is instead of bracket-specific rewards, merge it with solo queue. This would solve the issue of there not being soloq on icecrown. And it would motivate players to make 3s teams to gain an advantage. Just my two cents.
I'm really looking forward to the whole crossrealm thing by the way, keep up the good work!