>>6794387>>6794412>>6794430>>6796608Mega already made trainers. The sets were co-produced by Bandai for the Japanese market. My guess is that they never came over to the States due to licensing rights being held by another company. We got (ugh) Ionix instead.
If they do make new trainers, I hope they'll be at Monster High scale. I mean, scale is already kind of screwy, but it would look even weirder if the Pokemon were the same height as the trainers or taller.