Hmmm, i just so happened to fall accross this yesterday. The new ball coaster being developed by Intamin. It seems that Intamin are developing a new "ball Coaster" concept, very much like the 4d, although seating is slightly diffrent meaning the ride experience may be slightly diffrent. Passengers sit back to back, as you can see in some of the pictures below. 
http://www.coastersandmore.com/pic/eas05/ballcoaster1s 
http://www.coastersandmore.com/pic/eas05/ballcoaster2s 
http://www.coastersandmore.com/pic/eas05/ballcoaster3s 
http://www.coastersandmore.com/pic/eas05/ballcoaster4s 
http://www.coastersandmore.com/pic/eas05/ballcoaster5s 
http://www.coastersandmore.com/pic/eas05/ballcoaster6s 
It looks like it wont have to be to big. It also looks very much like the 4d coaster.
            
                                             
                    
                            
                                
                            
                        
                            
                                
                            
                        