Next Legendary Raid Boss?
Sure, we all know Deoxys Attack is coming, but what is replacing Cresselia after 4 PM tomorrow? Let the rampant speculation begin.
One or more of the Lake trio is possible, but replacing a defense heavy psychic pokemon with a trio of psychic pokemon with different strengths seems very anticlimactic.
Dialga, or, more likely, Palkia, would be awesome. And of course, we're still waiting for shiny Groudon and shiny Rayquaza.
A revisit from Latios and Latias wouldn't be a horrible thing, given that we now know they can be really good for PvP.
And Regigigas hasn't been out yet. Nor Heatran. I doubt they will have Mythic pokemon be raid bosses, so that rules out a lot of other stuff.
So, where are you putting your (figurative) money?
Answers
The lake trio seems very likely because Niantic rarely features legendaries in promo material without releasing them soon afterwards. It happened with Groudon and Kyogre, it happened with Giratina, I can't really think of an example where they teased a legendary and didn't release it.
The only good thing about them as far as I can see is that Uxie is the second best psychic mon for Great league but you don't need to get lucky with a trade to score one below 1500cp, it's always below the cp limit from unboosted raids. Azelf is strictly inferior to Mewtwo and Mesprit is kind of pointless in all ways.
Not excited for the idea of 3 months of them, no matter when they come.