NINJA and ROGUE confirmed

[Reynhart]

Exactly, they already have it. Which is why people are sure its for Rogue/Ninja.

I still don't understand how datamining 2.28 can prove traits for a 2.4 class.

One thing I thought for Rogue is giving it pretty useful cross-class skills. The whole "there's not point in playing a class past lvl30" is perhaps something that bothers the dev team, and they can try to balance the two.
Which can tie to the "support" role some people mentioned. Good buffs or debuffs available for Rogue could make it really interesting to play even without a Relic.

Or...In the live letter, they talked about Rogue mechanic based on combo (If I recall correctly). Imagine a trait that boost damage based on the number of different combos you made, and Rogue having access to cross-class skills that combo, like Impulse Drive->Disembowel...which could fit quite well with Rogue since Impulse Drive is more powerful from the back and disembowel just sound like fighting dirty