Indeed, there are big questions over the backhaul capacity. LTE may have a lot more air interface capacity, but how do you backhaul that from a remote rural location?
Questions from who? Considering their partnership with BT to run backhaul/last mile for LTE why would this be an issue? There's the other really obvious point that they are currently using cities for rollout where they have huge network hubs as well so it would seem lack of capacity on is low on the list of issues.