Rogue's identity used to be the combo class.
That has gotten nerfed repeatedly to the point where it's not an identity of the class anymore. Other classes can do better combos at this point.
It used to be tempo class too but that got nerfed as well and also continues to get nerfed.
It used to be the stealth class but then they nerfed Master of Disguise and Conceal.
It used to be the burst class but then they nerfed Bladeflurry. Now they have decent burst at best, not even better than Shaman or Mage in that regard.
Rogue doesn't have heals, board clears (it did have them with Bladeflurry and Dark Iron Skulker but that's getting taken out too), statted minions, buffs, taunts, chargers, windfuries, good weapons, weapon buffs, good hard removal (still relying on Assassinate since god damn Basic era),
They have mediocre draw, mediocre value cards, mediocre stealth cards, mediocre deathreattle cards and mediocre burst. Their actual draw options are Fan of Knives and Sprint... they have to rely on neutrals like Auctioneer/Drake/Thalnos to draw. With Conceal and Drake gone, they are severely hurt in the draw department too.
They have a "combo" mechanic but their combo these days is usually just a glorified Battlecry or condition. There is no real synergy among all the combo cards save for Vancleef.
Probably their biggest strength is their ability to cheat mana for tempo especially now that they have Counterfeit Coin. It's like a less stable but more aggressive form of mana acceleration where they can dump their hand and get an advantage but if it gets answered they auto lose the game. That's not a healthy mechanic to design the class around. They also have a strong tempo removal in Sap. But again, these mechanics are hard to balance around and get out of hand too quickly if you give them support. So this is not the identity that Blizzard is willing to pursue.
Blizzard wants tricky, deathrattle, "stealth" and pick pocket Rogue to be a thing. By Tricky they most probably mean the type of Rogue that likes to bounce cards around from their hand via stuff like Shadowstep, Shadowcaster and Ferryman. Deathrattle Rogue always kinda flounders because of the lack of defensive options and a lot of their strong deathrattle minions are leaving Standard soon (Anubarak, Unearthed Raptor and Tomb Pillager). Pick Pocket Rogue is successful only in making people salty, it should never really be a competitive tier 1 deck or else the community would riot harder than when they rioted against Shaman and Yogg. Stealth is something that they want to do clearly with the more recent cards but it's just going to be another minion tempo/curve deck where Rogue will play stealth minions on curve and get some synergy going. It's not really fun and interactive to deal with a board full of stealthed minions so Blizzard can't make this too strong either.