I think it would be good to have another Alton Towers Live concert but with different acts this time around. The concert was fantastic this year and worked really well so seeing this become an annual event would be a huge positive for the park.
Then on top of this they could have a second concert like they did with the Black Eyed Peas this year. Whether or not they do though will depend of what they thought of ticket sales for this years concerts and if it is financially viable to hold more than one.
I suspect there will be at least one concert next year at Towers, and if there is only one then an Alton Towers Live format please! As for an individual artist, it won't happen as she's already been touring for a long time and it will be over by next summer but Katy Perry as she is the definition of awesome!