Yep it was obvious they would be the intro deck foil rare, because they are rare instead of Mythic (all legends are now Mythic), and they dont put Mythics in intro decks.
I have had good success with Primordial Hydra mostly because my opponents use up all thier removal and have nothing against it. It beats down RDW hard if you get at least 6 counters on it (easy to do in green)
Even Modern Masters failed to get new people into the modern format
Intro packs can have good cards in them
Clot Sliver
Crypt Sliver
Toxin Sliver
Crystalline Sliver
Hibernation Sliver
Heart Sliver
Pulmonic Sliver
Slivers as they are now have no way to protect themselves.
Cant see a Sliver deck as it is currently doing well in at a FNM like that
It looks like they just did a single black and a single blue sliver just so they can say they are all five colors
Kalonian however depends on what else is in play with counters.
Every deck using green will be using it.
Gateway promos are giving to advanced level stores as free giveaways.