The Interference/WMG

The Time Devourer will be the next story arc's Big Bad, after Alex takes care of the current Big Bads
The Time Devourer has been stated to exist 'outside of time and space'. Thanks to the way the story is set up, all the worlds that Alex has visited are connected, much in the manner of Kingdom Hearts, including the future of Chrono Trigger, Chrono Cross. Which means that the Time Devourer exists outside all of their times and spaces too!

Besides, wouldn't it just be that awesome to have the Time Devourer as an overarching BBEG?