I find it very interesting that John Wardley all but confirmed that Project Horizon is SW9!
Assuming the ride is a coaster (and in fairness, I think it’s extremely likely to be one at this point; all the evidence points towards a coaster, in my view), I wouldn’t be surprised to see a coaster with stronger dark ride elements (think of something along the lines of Harry Potter and the Escape from Gringotts at Universal Orlando, or perhaps Arthur at Europa Park).
This type of ride might lend itself more to the “impressive coaster technology” that John Wardley previously alluded to, as a dark ride-style coaster could lend itself to trick tracks and such.
The smaller ground space compared to other indoor coasters could possibly be more fitting of something with a greater dark ride focus. Dark rides typically take up less ground space than coasters, so Project Horizon being a coaster with a heavy dark ride element and the odd high bit of thrilling coaster track would explain the tall building and somewhat smaller ground space compared to other indoor coasters.
Furthermore, it would offer an experience that would perhaps fill more of a hole within Alton Towers’ current lineup than a regular coaster in a shed would. The way I see it is that something like Gringotts or Arthur, which would have a stronger dark ride element with bursts of coaster sprinkled here and there, could feasibly pass as a dark ride as well and offer a similar type of experience to a major dark ride while also having plenty of coaster fun in there too. Whereas a regular coaster that’s enclosed, while it could also fill gaps in terms of being a family thrill coaster to complement RMT (dependent on thrill level pursued) and an enclosed coaster, would perhaps do that less.
If Project Horizon were to be that type of coaster, it could also explain Alton Towers’ general reluctance to refer to the ride as a roller coaster in the planning application.