The main problem Gardevoir decks have is having an energised and attacking M Gardevoir EX get KOed, losing 3 energy in the process.
Max Potion is mainly run to ensure you don't lose your Energy bank too quickly.
Once Roaring Skies comes out, Mega Turbo will be able to accomplish largely the same goal. It will also be slightly faster than Max Potion builds, but it will lose some mid/lategame stability due to having to give up more prizes, in general, than current builds.
So yes, I think M Gardevoir EX will stay relevant even after Max Potion rotatoes.