I'm a fan of the first Shaymin. Allow me to tell you that back in the 2004 format, Sandstorm Dunsparce was what you wanted to lead with so badly, and this card's not too much of an exception. The only difference was that in the current format, you couldn't attack on the very first turn of the game and you are limited to different types on this Shaymin. I hardly care about the ladder condition because you're searching for support pokemon that might be a different type from your main attacker (BKT Octillery is a good example, as he won't probably be the same type as your Beldum or Cosmog or Ralts for that matter. Infact, as for Ralts, you still have the Psychic one from BKT, so you can search for 2 Ralts that way!) It's gotta be good somewhere, most likely once Brigette rotates or when certain decks don't use Supporters to set up their bench.
However, there's a huge difference between 3 pokemon and 2 pokemon, and if we were using Call for family on previous pokemon to set up our bench, then the same would apply for the Sky Form, bu we don't, so I don't think Sky Form will see any play.