If such a thing was to be done, it'd be nerfed immensely. As in duration period of 3-5sec at best. Enough time to get the one cast off, if not most of one (enough time to move if needed and stand stationary before buff wears off). The reason being is how casters do not have to worry about TP use, so Sprint is essentially another get-away-always card while heavy damage/healing is inflicted/cured. Combine that with the fact that Swiftcast also exists and you have an almost always on upkeep of moving casters. So to further prevent that, the cooldown would have to be 2-3min as well.

Mind you, I'm not saying that even that would be a bad thing. In fact, I would quite enjoy the idea of it, it's just that as it currently stands, a 10sec free cast that's uninterruptable even while moving (that has a 30sec cooldown) sounds a little too... overpowered.