New feature for Aether Raids got announced out of the blue, adding a whole new set of tiers above 28 for those that hit Tiers 27 and 28 in early January. It's basically like the Great Summoner tier in standard Arena, only with more tiers to play around in. If your score falls below the threshold to hit the highest tier, 38, you plummet all the way back to Tier 23 next week, similar to how if you can't stay in Great Summoner, you're back in Tier 20.
However, Tier 23 is not tier the typical tier everyone starts at right now, 21; those who get into the Vault, but then drop out, have an 800 point advantage over the others to get back in the next week.
This feature will help section off the super competitive players in AR, those that will regularly smash the score caps, and gives them a cozy tier to play in and reap bundles of rewards. Those below them, the ones that cruise around tiers 21-27, meanwhile, won't have to continuously fight these super competitive players' crazy/auto-win Defense setups as they go up the tiers, so they benefit as well.
On another note, the next Tempest Trials login bonus starts on the reset after next. So, the silhouettes for the New Years units will be tonight, and the trailer proper will be tomorrow.