hold the phone. ur threat building stats. expertise/hit look great but when i flipped over to ur defense i freaked. granted u r wearing the merc chest. but u only have 472 defense and ur dodge and parry are 15%. ur block seems fine. but ur dodge is WAY to low if u r gonne be hitting vashj and kael like u should.
u ahve 37 expertise wow that is amazing. imo i would drop ur Shard of sontempt and put on a Defense trinket of some sort. u need to balance ur gear a little more for defense and a little less on threat gain. using proper ability rotations with those stats u could push like 1400+ tps all the time. but ur gonna get hit like a truck cuz of the low dodge.
Your defense looks fine, chants look good, I might consider trying to replace the shield with the one from Gruul, or out of ZA, but not super critical. (Armory is down for me atm, so this is off armory lite, gear may be different.)
As long as you have 40-45% total avoidance I think you are set for t5 especially with that amount of expertise and as long as your hp/armor totals are good I wouldn't touch anything for now.
1400+tps is not easy to obtain, it requires absolute perfect group make ups, so no, your threat can ALWAYS go up, trust your dps and ask them how much they hold back and you'll see. Adding a bit more avoidance could help but it isn't as bad as Tizack states, you're still relying on a random chance of it coming, you won't get hit any less like a truck with 15 or 20% dodge, you'll just space out how often you get hit, which is always important but You look fine for now.