The "moving interrupts casting" is an appropriate mechanic if your game functions on a near 1:1 server/client ratio (ala World of Warcraft.) Unfortunately, with the terrible server/client relationship of XIV, the moving while casting is quite meddlesome.

As it stands, I'd rather have them keep casting the way it is now and then ensure that we don't have to deal with INERTIA at all in 2.0. This way, the stop/go/jump/cancel nature of the game will be intuitive and won't have awkward pauses or barriers before you can begin to cast. Inertia is/was just a terrible idea in the first place.