The last developer update announced the future release of the Experimental Mode with many tests related to balance changes and game mode modifications. This new feature will allow these changes to be experienced by the largest number of people on Overwatch's live servers. On February 24, Jeff Kaplan announced that the first experimentation should arrive the next day (January 25) with the testing of a major change on the Role Queue: the Triple DPS.
Triple DPS
Jeff had already talked about it on the forums: teams were testing the Triple DPS composition — one Tank, three DPS and two Supports. It would considerably reduce the queue times for DPS players, as they would be present in greater numbers in the compositions. The least represented category (i.e. Tanks) would see the number of players needed per game reduced by half.
This reduction in DPS queue times is a priority for teams, and this new composition could be the answer. With this Experimental Mode, the developers allow us to discover this potential change and to see what the community thinks about it. The statistics of the effect of this new composition on the queue times will be analyzed by the developers, in order to see the real impact in-game.
Off-Tanks
In addition to this new composition, it was extremely important to define the role of the off-tanks — which would lose all their interest in this new configuration. It's done with Jeff's announcement of the redesign D.Va, Roadhog and Zarya. These changes were necessary to allow the 1-3-2 to exist.
Watch out! These changes won't necessarily be released in-game, unless the 1-3-2 is adopted later.
The Experimental Mode will allow you to win levels and the victories will count for all the events in-game, such as Ashe Mardi Gras challenge — which should arrive at the same time as the Triple DPS test.