iOS 6 Wifi Plus Cellular

So apparently Apple as introduced a "Wifi plus Cellular" option for data in iOS 6. The idea is that data can be sourced primarily via Wifi but if Wifi is spotty it can be backed up by using the cellular connection as well. While this idea sounds great I am not sure how well it will work in practice. Firstly, how many applications are designed to take advantage of such redundant connections resolving to different IP addresses and the like. Unless the switch over is transparent and instantaneous, more time may be lost with flipping and application recovery than is gained by the dual channel feature. Ideally I'd like to see the feature go further and say bind specific applications to either Cellular only, Wifi only or both. Consider the situation where you are using your phone for work, you'd like your work emails to come through immediately but you're probably not too concerned if Facebook updates slowly in the background. Secondly it will be interesting to see how the carriers respond to this, there are lots of efforts underway to push users off the RAN and onto Wifi, this setting will ensure that a user on Wifi still consumes cellular resources beyond those required for voice termination. This is particularly a factor in networks where voice is still circuit switched but data is packet switched.