I'd love to see an indoor rollercoaster at Alton, especially there as it would join up to the entertainments complex but I don't think a space theme would suit Forbidden Valley - maybe if it was themed like the Disneyland Paris version, but even then I still don't think it would look right.
If it were to be a thrill ride I think a Eurofighter (think that's the name?) would be amazing in the dark with the fast flowing shuttle's, steep drops and sharp turns and inversions!
Maybe Adventureland / Storybook Land would be another location? Although that would have to be a family coaster.
Well indoor rollercoastes require a large building & Im not ure weather there is enough room in storybook land, but is it a small possibility. Im also not sure about a eurofighter as it sounds like SW7 will be one of those. But gerstlaur (however you spell it) is a possibility for manufacturer.
And yes, thinking abot it now a space mountain looking ride is a little too much like copying disney, so why not have lton be unique? Heres a little idea I made to try & fit it in with air:
As you can see, its a HUGE building, but lowered into the ground a little, it should be below tree height, although I stil imagine it'd be difficult to get planning permission. But its an Idea!