Until recently, WAR's scenario lineup was changed with each major patch version. That happened every few months, so the lineup ended up getting pretty stale. That is now no longer the case. Instead of changing with each patch, the lineup will change weekly, albeit slightly.
All three scenario brackets will also now share the same set of four scenarios. It used to be that each bracket had its own set. To cut down on the amount of work needed to be done, it makes sense that they would all now have the same scenarios to choose from.
The new system is: Once per week, the oldest scenario in the lineup will be removed, and a new one will be added. On the weekends, there will be an additional Weekend Warfront scenario added to the list for a total of 5 to choose from.
I am pretty pleased with this direction. One of WAR's strengths is the amount and diversity of scenarios it has to offer. Having a rotating lineup will help to keep things fresh instead of having to wait months for a change. Grovod Cavern, the Play as Monster scenario, was also changed to encompass all of the tiers, which lets everyone play together.