Depending on how agressive the meta ends up, Rogue may need the extra tempo and removal that Shadowblade can offer. People play Gluttonous Ooze over Acidic Swamp Ooze just because the the 3 or 4 armor it can give you, so why not play this and save 5 health when killing Aya Blackpaw that you would have taken from Hero Power Backstab.
It would be a dream if this cost 2 mana ? But well immune, maybe, compensates. It's finally a good weapon for Rogue. They should rename it for The One, so can be easily pun with: Hey did you saw that new The One weapon? - What? How is it? Yes, it's truly The Rogue One.
I've seen it in a mill deck; the rogue plays Vanish to clear the board and overfill your hand, valeera, then the Shadowblade and games with repeating Coldlight Oracle again and again. It takes both decks to fatigue, but the rogue is immune.
I don't think I've ever seen it actually win the game, but it's a neat idea.
It's not like you couldn't do it with Violet Illusionist. Anyway, Shadowblade proved not to be that essential, as RKLS noted, SI:7 Agent is still a better choice, at least until they provide some more buffs or tutor cards for buffs or whatever it actually needs.