With the idea that the Necromancer is an Int based class, if Druid were released as a strength based class; I think it makes the most sense if Blizzard went either a ranged melee class similar to the Amazon, or something more stealth like such as a rogue.
The idea of a class built around duel wielding daggers like a rogue intrigues me because the concept is already in the game. Daggers naturally roll lower DPS than any other weapon in the game, and they could use that to their advantage when creating duel dagger synergies in the sets or passive skills even. Imagine one of the first passives you unlock is a 50% damage bonus while duel wielding daggers...or something along those lines. Something like this would make legendary daggers viable to use on hand and not "cube only" options which right now seems to be an issue in the game.
Also, having this idea of a stealth or surprise could be an interesting mechanic within the game.
Since the Necromancer had 3 properties as well when being developed, I will do the same here. I think the following things to keep in mind here when designing the Rogue/Shadow class are as follows:
1. Dagger Mastery
The combo aspect could be a very new and exciting introduction to D3's current playstyle. If there were certain skills that triggered other skills via runes or even passives, this could be a really cool concept. Balancing could potentially be an issue though.