But that's not quite what's going on. As explained by community manager Elrar quite some time ago, trial servers are lower-population servers that are essentially being put to one side for large-scale trial programs. Character creation for subscribers is disabled on those servers, and there's a message encouraging you to move to another server with a free transfer, but it's not a shutdown, just a ramp-up to a larger trial period for non-subscribers.
According to Rift Junkies, a total of 11 servers are seeing the trial tag applied, and players are encouraged to move off these servers by January 18th. If you've got a character on Belmont, Galena, Atrophinius, Crucia, Alsbeth, Estrael, Shadefallen, Sunrest, Freeholme, Dayblind, or Faemyst, now would be a good time to start planning for greener, non-trial pastures.
[Thanks to Celestial Lord for the tip!]