This may be a little imminent for the Futurism Topic, but hear me out.
This also may be over-speculating, but remember how the Legendary Birds got an exclusive move during their Raid Days and the Ultra Bonus Week? (Articuno = Hurricane, Zapdos = Thunder Shock, Moltres = Sky Attack)? I was thinking that the Legendary Beasts might as well despite no announcement, so I decided to look at the move pools to see what they could be. I actually got a few hits:
Raikou could learn Spark instead of Thunder Shock or Volt Switch. According to simulations, Spark is SLIGHTLY better than Thunder Shock.
Entei could learn Ember instead of Fire Fang or Fire Spin. Sure. This wouldn’t improve it, but neither did Hurricane for Articuno.
Suicune could learn Waterfall instead of Extrasensory or Snarl. This would vastly improve Suicune. While it would still pale in comparison to other Water-type attackers, it would still greatly improve it from where it currently sits.
Like I said, this might not happen at all, but it would be interesting if they did since they did that for their days last year. Also, every other Raid Day (except Articuno at first) got an exclusive move, or in some cases, two exclusive moves.