IOS VB and VVB are pretty similar and it's suppose to allow you to seamlessly migrate from IOS VB for feature parity. But there are some differences...
With VVB, you can get Real-Time Reporting, RTMT Support, and Prime Support. Goes without saying how great it is to have Real-Time Reporting and RTMT for those supporting the contact center environment.
With VVB, you can have peak global concurrent sessions, which is independent of the number of queuing locations where as IOS VB you'll need licenses budgeted for peak sessions at all gateways.
From a redundancy perspective, if you want more IOS VBs, you'll need more gateways which means more licenses ($$$). With VVB, you're free to deploy as many VVB VM guests as you desire.
From a license perspective, the IOS VB licenses are tied to the ISR hardware and would need to be re-purchased with new hardware. With VVB, it's perpetual licenses (use the licensed software indefinitely), and allows you upgrades with a SWSS contract.
With IOS VB, you need physical ISR hardware, which is pricey... with VVB, you just fire up a new VM guest.
As you can see, without the dependency of ISR hardware and the headaches that is Cisco licensing, VVB is far more cost effective than IOS VB. I'm sure Cisco will continue to add features since VVB is a scalable application. In short... it's a good thing :)
