Giving old pokemon a viable egg move would help discourage the transfer and usage of pre-gen 6 Pokemon. On topic, Tail Glow Mareep.
Tail Glow would be pretty bad as an Egg Move. There's nothing in Mareep's egg groups that can learn Tail Glow outside of Smeargle, and an egg move that actually requires Smeargle to get would kind of suck. Unless a new pokemon in the Field / Monster groups is introduced that learns Tail Glow, of course.
I'd say Drill Run for Escavalier, but that's kind of the same problem, except that nothing in its egg groups learn it without a Tutor from Gen5. That and it should really just learn it from the tutor itself because seriously why doesn't it, hands are giant spear drills.
So Quiver Dance (and / or Bug Buzz) for Flygon. Might be kind of weird to imagine Trapinch dancing, but egg moves sometimes are a bit weird.
~ Master of Electricity ~ Electro: 0518-6613-7620 - Pokemon White