DD wanted to die undefeated and just pass along the now, normal Elder Wand to Snape. When I say "normal", I mean the EW stripped of all its extra ordinary powers.
I don't think DD planned for Snape's murder. For one thing, he would have felt much more remorse for his death than he shows to Harry in the King's Cross chapter.
He says, 'Poor Severus...' which shows that he's sorry for Snape.
But if he had himself planned Snape's death right from the beginning...wouldn't he have shown guilt. Look at his reaction to Ariana's death. He wouldn't ever have wanted to repeat Ariana ever again.
He didn't want Harry to have the Elder Wand too. And anyways, it would have been useless to him, if DD's original plan had worked.
And DD said in King's Cross chapter: If you possessed them, I wanted you to possess them safely.
If DD's original plan had worked, and if Harry had got the EW, then he could possess it safely since its power is gone.
Maybe he thought Harry would need it to unite the Deathly Hallows..and thus anted Snape to pass it on to Harry?