Its going to be big.. but it might not be tall, the corkscrew only just got planning permision, even then the highest point had to be painted green. Its no suprise the Corkscrew is closing this year, the design life and fatigue life of the many welds etc would have been 30 years, given many of these were done during 1978/79 its no wonder its end of life for the Corkscrew.
However anyone wandering round "Ug" land last year may have noticed the signs of some serious civil engengineering/geotechnical happening as the park came to a close in the weekday evenings while it was still sunny. Test boring equipment seen on its way to the path which runs front of towers to back of UG land. A leica lidar has also been seen being set up in UG land.
Those with a keen eye over the last few weeks may have even noticed the reflective targets left behind on structures, one can assume every structure, tree and building is now in some massive computer CAD model, ready for a coaster development team to drop in something very very big ;) Given the recent leaps in computing power and CAD packages able to hold massive models in memory you can now wrap a coaster round the landscape.
Back in the 70's and 80's you could only design a coaster on an empty or near empty space. Its why the CorkScrew was built and tested a Vekoma, taken to bits and bolted together on an almost clear patch of ground. Move forward to Nemiss and you know what shape hole to dig. Forward again to Rita Queen of speed and you can fit it in part round existing structures (example, the interesting work round the cork screw station).
So if the current Corkscrew area is just the load/unload area of a much bigger ride... Whatever it is needs a good rider throughput, say 1000 to 2000 riders an hour, its got to be a first, so its not going to be in the public
Vekoma etc price list (like you can buy yourself a Hex aka Vekoma Madhouse-78). Loading needs to be quick (air problems), and its got to be visable (black hole hidden in a big tent).
One thought, and I'll let a few others post some ideas first, is I've found a few recent patent applications relating to... Multi-track roller coasters designs which match nothing I've yet seen built... The online search at the patent office is one good source of coaster rumours ;) One such patent covers the use of LIM motors and holographic projection methods making the track near invisable to the riders...
The use of LIM is interesting as it means the ride can get a speed boost a halfway point....