I think the most I've ever had sprinting straight back to the middle was ~1 second of invincibility, and that itself is very iffy. Unless they are in your side of the map I really don't see this being as huge of a game changer as its being made out to be.

And most healers sprinting back are going to be using oGCDs or anything instant anyways to immediately top or try to top someone off. So unless the enemy is already on your bridge/side this isn't changing much. But I could have sworn it was supposed to cancel on action anyways. *shrug*