Alternately, Emet-Selch is in Solus like we currently assume, and G'raha has traveled back in time from The Future™ to warn us of things to come (getting a bit crystally in the process), after waking up and realizing that we done broke it. This could have something to do with the calamity Salina foresaw and her true plan for the Crystal Tower, or it could be him trying to undo the mistake of thinking he needed to use the Tower to travel further down the timeline when really he just needed to join the Warrior of Light's band of exceedingly competent merry men. Since G'raha's arc was loosely patterned off of Desch from FFIII, "coming back to save us when no one else can, after we thought he was gone forever" would be a perfectly valid card to play without invalidating any established references.

Or he could even do all that and then get bodyjacked by Elidibus after he leaves Zenos, because the last heir to the Royal Allagan blood is almost certainly too sweet a host to pass up.

Of course, we technically don't know who that is, but the facial structure and voice from the future stuff going on have suddenly made G'raha Tia the Occam's Razor answer to the question of who is under that hood.