So what do you think the featured cards in the theme decks are going to be? The 3 starters or the 2 legendaries?
Heartgold Soulsilver had the 3 starters, but there was not really a Ho-oh and Lugia card that isn't some sort of special card.
Boundaries crossed had the legendaries, well the video game cover Pokemon, and didn't want to reuse the Unova starters as cover Pokemon.
In both Generation 4 and Generation 5, the first set had the starters while the fourth set had the legendaries as the theme deck cover cards.
In Generation 6, due to the nature of the simultaneous video game release and the not so simultaneous TCG releases, we got Kalos starter set instead of Legendary Treasures theme decks. The Kalos starter sets are kind of like theme decks, but they aren't, and at the same time, they represent the starters of Kalos. Not to be redundant, the first XY set didn't have the starters as theme deck cover cards, but instead did the 2 legendaries.
I guess the only way to tell what the theme deck cover cards will be for this set is to see what is in the set.
It would be way from left field if the Theme Deck cover cards were neither the 3 starters or the 2 legendaries.