Spinball effectively had no exit on busy days, with RAP taking up one side of the path and FT the other. I think simply swapping FT & SRQ would have helped, as if the small exit queue was full that'd be a pretty long wait for SRQ and people just wouldn't wait that long. Unfortunately they took the simple option and removed it entirely - a real shame on wet-weather days when it's 3 per car and most go out with just 2 people on board.
It was rumoured that Spinball's SRQ would return at the same time as the Smiler one did, as it wouldn't have required an extra staff member to manage it, but it never happened.
Rita's and Thirteen's won't come back as they'd need to re-introduce a merge host (£££). Oblivion could (in theory) regain a SRQ without increasing the staffing cost, but with good batching you should never have more than 1 empty seat per shuttle anyway. WM has no space for an SRQ - you don't know group sizes until batching in the station and there's no way to bring single riders in at that stage.