In my opinion, it's a tricky time for Megas that aren't named Rayquaza or Groudon (Though I personally hate the latter) at the moment, because not only do you have Giratina shutting down damage and their Spirit Links, but you've got Regice/Vileplume which can really slow down Spirit Links, Mega Turbos and so on as well as locking out all damage. Plus, Resistance Blizzard isn't an ability that can be sealed through Silent Lab or Hex Maniac, making it harder to combat. So, it kind of seems like the counters to a deck like Glalie are pretty high, but I really want to see the deck do well because the attacks are so unique and interesting.
Considering a few of the decks going around, there are lots of decks that rely on the 2HKO rather than the 1HKO. Manectric, for example, or Vespiquen (who can't hit Glalie for weakness) or even Giratina rely on 2HKOs to win games, and 2HKOing M-Glalie with these decks involves putting 10 damage counters on it- Cryomouth territory. So I think it has potential, but the deck will have to run quite a few checks against the decks it's weak to, which are quite a few at the moment.
I think Shrine of Memories is a great idea- wear them down with hand-match Instant Freeze, then hit with Cryomouth for a 2HKO on everything. Then, when Glalie's HP gets low, Cryomouth Crymouth Cryomouth. Raichu may be a good addition to the deck, or the aforementioned Articuno (Maybe with EXP Share?) or Zoroark.