I believe RMC are fully booked for 2017, so if it is them, and Alton have booked them in pretty sure after the effort of trying to make a coaster there they wouldn't cancel, only reason I see this being cancelled is if it was RMC and afterwards they approached with that new track concept for somewhere else on park, so they delayed this. I still feel like it will go ahead in 2017, a coaster at Alton, in that area could take a bit longer than average to plan due to restrictions I'd think. Timeline would be something like 2017 opening construction through all of 2016 and early 2017 which means plans would probably go in between now and January/February, 2015 would be trying to get the best possible design to be given permission (probably the start of the year as well considering that Environmental impact assessment went in, and planning would have taken place in between September 2014 and around now, with a company being approached before or in that time, probably earlier this year I'd think. I wouldn't be surprised if they got to work on this not much time after the smiler opened. This is just an estimate/speculation of what I think it would take for a coaster of this description in that area, of anything is a long way off let me know, I'm pretty sure unless it has been completely cancelled it would go ahead, as Whatever company is going to make SW8 would have a spare booking which by now could be quite hard to replace for 2017. One of the main reasons attendance is down is because they haven't added anything for thrill seekers for two seasons as the smiler was expected to bring people in over that time but for obvious reasons it's only been open for around one full season and 3/4 over 3 years. They can't wait for attendance to magically go up before they open a coaster, the reason it isn't going up is because it's needed for them, the sooner the better.
If SW8 is delayed, 2020s major investment will probably be delayed as well, which could be a problem with a single ride in 2021 competing against what could be this country's potentially best theme park, and I think they'd want that to take the limelight for the year it opens, which is why I think major investment is happening over the next 5
Years I reckon we'll see 2016- Thorpe
2017 Alton, but a large refurbishment and a new medium ride at chessington 2018 small for Alton and chessington medium for Thorpe and 2019 coaster for Thorpe 2020 new flagship at chessington and dark at Alton.
If SW8 doesn't go ahead 2017 it could cause problems with all parks potentially