Because of the way the DW works, movesets are all basically tentative. Ponyta gets Heat Wave, a gen IV tutor only move, in the DW, depending on the score you get in the mini game you play with it. A male DW ponyta with Heat Wave can breed with a female DW flame-body ponyta, resulting in about half of babies having the Flame Body ability and all of them having Heat Wave. So, I wouldn't completely rule out Signal Beam/Trick Magic Mirror Espeon, but I also wouldn't plan on it. It could even end up with something ridiculous like Butterfly Dance lol.
Anyways, I gotta say I feel like lead Espeon is a bad idea because it will just get wrecked by most other leads. Specs is a pretty good idea as Magic Mirror is really best when you're switching in and out, because then your opponent has no idea when their status/hazard is going to get reflected on them. Just one proper Magic Mirror switch-in reflection could really get into your opponent's head, perhaps even forcing them to play a more aggressive style.