GoldCyndaquil
Shiny Hunter
Considering that Calem/Serena were much more serious trainers than Brendan/May, I think Brendan/May are less likely to be given Mega Evolutions. Now Wally might Mega Evolve, but he wouldn't be as interesting because we already saw Mega Gardevoir in XY. Unless he gets the third starter and Mega Evolves that.
Or they could just give Gallade a Mega and Wally could swap out his Gardevoir for a Gallade.