The amount of people that believe you can only have one Mega on your team is abnormal.

>There is the official web info.
>There is Coro-Coro
>There are the leaks.

It's never been hinted that you can only use a Mega.

If the trainer could equip items, and that item is a Mega-Stone, then you could only have a Mega.
But no, it's an item you equip on your pokemon, you can have 6 fucking megas.