The project had been a VR project long before Derren Brown was confirmed to be onboard. There were other themes for the ride considered; almost all of them were not IPs as well. Merlin's market research had shown interest in a Derren Brown / illusion based ridew and there were a couple of other options considered for a 'Derren Brown attraction' (even a wooden coaster was considered at one point, for example). So when Derren was bought on board to Ghost Train, it had already been decided to be VR and the basic principle (get on a vehicle, get off for live action sequence, got on again) was there too.
Simworx offer a lot of effects which could be installed on the train carriages, or be used to move the carriage (for example, the train shudders slightly when a ghost breaks the window in the first VR sequence). Many were considered (like window misters, etc), but most didn't make it to the final implementation phase. The only one which was bought but never used were leg ticklers; something which was never installed and the park got rid of them in early 2017.
The original plan was that the screens on the train would effectively play the same footage as the headsets. This would allow staff to see what was happening, and also meant anyone who was too scared/uncomfortable with the VR could still see the footage.
This later changed to the loop we have now, again for the impression that if people didn't like the VR they could still watch something. But then they realised how bad the experience would be just sat in the dark watching the screen and seeing staff touching people. So they scrapped the idea of allowing people to take headsets off and just encourage them to close their eyes.
Ghost Train has all been a mess really. Simworx completely over-promised what they could do, and severely under-delivered. Thorpe underestimated the amount of money that would need to be invested into the VR aspect. Too little thought was put into the operations of the ride when it was being designed, leaving the park with something which is extremely difficult to operate correctly/well. Derren isn't exactly fond of the experience, has had some problems with how Merlin and Thorpe handled certain aspects. It's all just not great.
The park have certainly considered dropping the VR element altogether. Even from late 2015 the park have had a back up plan should the VR completely fail. But the trouble is, dropping the VR either means they would need to spend a fair amount of money turning it into a decent-ish simulator, or going cheap and being left with a ride that isn't much better. And we all know what option they would go towards...
