I've just realised there may be some method to this madness.
Based on current statistics and recent trends, it is unlikely the Derren Brown ride will open until May. This leaves the start of the season with 2-3 months without the new attraction, which could lead to lower gate figures.
As a result of trying to maintain gate figures at the start of the season and keep interest going, Containment will be used as some form of sweetener to keep the ball rolling.
In other words, Containment could well be used in a way that Sanctuary was whilst the Smiler was undergoining final touches before opening.