The park did trial single rider on Saw in 2009, 2010 and maybe even 2011-12 (memory is hazy). In terms of filling up seats, it worked well. It was always a bit of an organisational faff though, since it didn't have the infrastructure set up for it to work.
As I understand it, this is something which has been pushed to be tried by some staff for a while. So this is serving as a trial period to see if it works at improving utilisation scores (ie number of seats filled), and how it works from a practical / organisation standpoint. Then maybe they can go from there.
The issue the park will face is the same they have always faced - the majority of the park's rides aren't designed with a single rider queue in place. Really, Stealth is the only one which has the infrastructure to do it properly and not interfere with Fastrack / Ride Access Pass queues and ride exits. The current Exodus plans don't show a single rider queue either (though these can of course be changed).
So yeah, hopefully it works, and hopefully longer term the park can implement ways to make single rider queues work properly. But at the same time, it should be stressed this is just a trial, and even if it does go down well, there's no guarantee it will mean it stick.