As mentioned above, I'm absolutely certain more rides will be appearing.
One must remember Chessington has its zoo (and sea life) in addition to its selected rides open, whilst Thorpe doesn't, so the park will likely be looking at opening as many rides for this event (that are feed able to operate).
In addition to what's already been announced, I believe Inferno, Detty, banana, Teqcups and X could do this well. I've even heard rumours of the Caroulsel staying (just for the event).