I have read that the V4 is slightly lighter and more compact than the V2. I suspect that Euro 5 emissions regulations may play a role in this change if it happens. The V4 will be more expensive to produce and to maintain. I have not ridden a V4 but all reviewers claim that it is much smoother than the V2. We are living in a time when some truly wonderful motorcycles are available. I am eagerly awaiting future anouncments.
The V4 is definitely not more compact than a V-twin. It's impossible. The V4 Panigale is significantly wider than the ole 1299. They claim they're trying to "show off" the V4 engine in the Panigale, but we all know that's just marketing spin for, "how do we make this negative a positive?"
It's nice that the firing order sounds like a V-twin, however I don't see the appeal. If it's a v4, I would prefer it to sound like an Aprilia. For a track bike, 97% of amateur riders can't even reach the limits of a 600cc... I don't know what any Ducati V4 riders do with them (cars and coffee? park it in the corners and freight train down the straights?).
I don't have any complaints with the smoothness of the V2. Frankly, it gives it some character. Sure it's a bit lumpy below 3000rpm, but who really rides there? The BMW S1000XR engine is smooth as butter and makes even more power than the MTS, and is completely soulless. I'm completely happy with the current engine output; it's almost too fast. I rarely get to rip on it for more than a couple seconds for fear of the fuzz, so why do I need even more power for? It sounds absolutely glorious at full chat, but then I look down and the speedo is reading XXX and I'm only in 3rd gear and I know the fun is over.
It would be nice to drop 30lbs, as Dave mentioned, however. The bike is just too damn heavy to do anything technical offroad, mainly due to it's shear mass. It's a beast to push around with luggage.