I'd say it's unlikely you'd get a Diablo legendary if you are half-way through the quests currently. Surely getting one requires a quest reset post-patch (which might even be available without having to complete the storyline).
Also, has anyone noticed any weird happenings with their quest reset availability? At one point a few days ago, I had been helping a friend level somewhere in Act 1 and 2, and my own storyline was only at Act 2 or something after my latest reset. After playing with her, I realized I was able to reset my quests. I guess this has no beneficial effect anymore (with leg being moved to Diablo), just thought it was interesting, and accelerated my SK legendary nicely for that run.