In light of recent events... there are NO plans for a UT weekend. Official post here.
Will this weekend have UT trading?!
When is the next UT trading weekend?!?
Will there ever be another UT weekend?!?!
Aww, man! Why not?
Un-soulbound weekends are special events that only happen when the time is right. When Kabam decides to have an UT weekend then they will post here to let everyone know! Until then, keep your eyes on the forum, the official Twitter feed, the official Facebook page, and /r/rotmg to make sure you find out as soon as it's announced.
The Kabam team understands the importance of UT items, both in terms of playing the game and trading with other players. However, due to many factors they've decided that UT items will be soul-bound for the greater good of the game for the time being. Maybe some day we'll all enjoy un-soulbound UT items permanently, but that unfortunately isn't today.
Until next time, happy hunting and be safe out there.