Personally, I wouldn't want to see another B&M Flyer. If another one of them were built less people would go to alton and air wouldn't be so unique. For the 2015 coaster i know it probably wont happen but I would like a 4D coaster. X2 looks amazing and now that Intamin are building Zacspins, I would say now is the right time to invest in one. Obviously wait and see if the one at MM is a success which im sure it will be.
Now to the realistic side of things....Seeing how there is only one standup coaster in Europe, it wouldn't surprise me if TP invested in one. It would bring visitors to the park as many people just cant be bothered to go to Drayton Manor, and anyway from what i have heard its rough and boring and i have also heard that B&M make pretty decent standups.
I doubt they would build a Mega coaster because they don't really have the room unless they made most of it over the lake, and then the residents would complain so i seriously doubt that.
So to conclude ,I think its going to be another B&M that we see at Thorpe Park in 2015 which is sure to please most of us CF'ers.