For me the possibility to enter the desert it depends if we enter Agate right now (I mean after the return to the city on e15) or not
I have the plot on my mind that there is a possible unerground path that leads on Agate from Meteor Base on Reborn Sewers and after that we clean Agate we have to go to Desert to clean the other one Pulse that probably is on the top of the Mirage Tower
Or something like that. The 2 Pulse (Sleep one and Barrier one) are somewhere on Agate and Mirage Tower, probably someone o Labraddora and one on Sewers. I think the final clash with Meteors will be on Mirage Tower or we will have and some plot later on the League