The game the way its setup right now, puts level 50's in the baby zones running around doing only FATES. The possibility of NM's coming in the future opens up the option of setting up a zone with Notorious Monsters for ATMA.
Basing each NM upon the name of the ATMA you're trying to attain.The zone should be large to have all the NM's spread out.
And there should be filler mobs of equivalent level but not as tough so you have to work to get to the NM. The NM should be 16 player minimum to defeat, with a minimum of 2-3 ATMA drop per group. (that way there is a chance that more players will stay instead of leaving.)
All in the hopes of putting level 50 characters back in level 50 zones, so that lower level characters have a better shot at exp.