I think any race/class combo is possible given that there is ample reason for gameplay. There's a lot of conflicting class combos, and they're explained by being rogues outside the main faction (Dark Iron mages/warlocks, Highborne mages) or a new offshoot that wasn't there before (gnome surgeons, sunwalkers).
Anything can be possible, from Draenei Warlocks to Forsaken paladins to Tauren Rogues. All you need is a bit of suspension of disbelief.
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