In terms of the format changes for the US series - I don't think the BBC will use all the ideas as it can be a rather confusing format.
I think they will implement the steal aspect, but it's the Live Shows which are an issue, there is nothing different about The X Factor and The Voice live shows which is a shame.
They were wanting to use less live shows this year because that's where it all fell apart, so I wouldn't be surprised to see the knockout round or at least have two battle rounds (for example each coach takes 12 from the blinds, 6 through the first battle, 3 through the second battle then into the live shows).
The question is ... what was it that caused it to be a relative flop? It doesn't really matter what the Americans changed - they need to make changes to the UK version that will make it more popular here.
I'd say the live shows were where it went wrong but some of it could be put down to dodgy scheduling. I'm sure some of the live shows went out at about 6pm on a hot summers Saturday. They should've tried to get it on air by January instead because they could potentially run straight into the same problem.
The live shows were very rushed and there wasn't really time to get to know the acts or see them develop. They lost far too many acts each week too, which didn't help with it feeling rushed. Some of them issues are even present on X Factor and that drags on for 10 weeks losing one a week (although it does fly by).
I do wish that ITV got the rights to the format instead, it seems like a natural evolution of the X Factor format (which in itself is flagging) and they tend to do big scale productions like this much better (speaking on the whole).