The snarky part of me thinks, well, they finally realized there's absolutely nothing distinctive about this airline to distinguish themselves from the US3 (well, aside from the fact that they can't match their operational reliability), so they might as well copy them... B6 started charging for "preferred" seats earlier this week. Seems to apply to window and aisle seats near the front of the plane. Applies to Blue and Blue Extra fares alike.

If it weren't for the fact that the A320 conversion was a total dumpster fire that took years to do, I'd think the next thing on the chopping block for them would be their generous coach leg room.

Here's an example from LGA-BOS: