Warlocks are great for boxing if you don't mind managing shards. I would strongly recommend doing some sort of mixed team, too, no matter what you plan to do with them. It's not hard to make them work the same as you're used to, and with buffs not stacking these days, you'll be more powerful. You just make castsequences so they are each doing similar things. So like if you had the warlock doing a shadowbolt, the priest might do a mind blast.

By the way, do you know what server you're going to roll on?