For every set that is released, an old set is dropped when the new Mod comes around:
EX: DS - EX: HL
EX: LM - EX: FrLg
Since Holon Phantoms is announced:
EX: HP - EX: TRR
The difference between DX-on and EM-on will be determined by the release date of Miracle Crystal. If it is released before Worlds, the format will be EX: EM-on. If it is released after Worlds, the format will be EX: DX-on.
Deoxys is a gray area for me. On one hand, I want them to get rid of Jirachi and Magcargo. On the other hand, I want them to keep Weezing, Claydol, and Shining Rayquaza...
My best guess is EX: EM-on, since there is barely enough time to squeeze another set through before Worlds. Holon Phantoms will be pre-released at the end of April. This leaves May, June, July, and the first half of August to release Miracle Crystal.