Oh, I get why a Summoner is a big ask. There's many reasons not to do one: hard to balance, action economy is tricky, the size of the class (it'll need a lot of it's own material, like stats for summons) not to mention what type of Summoner is it? A Necromancer, reanimating the dead? A Fey Summoner, shaping spirits into animals? The Psion forming Astral Constructs? Putting all those under one umbrella class seems like you'll run into the Mystic problem, the class is spread too thin and loses its identity.
That said, it does have a play style different that'll set it apart from the other classes, and it's certainly unique. Also, it's a class that can take some of the Lazy Warlord design space. And if we are going to see more crossing streams with Magic the Gathering, the game is centered on summoning creatures to fight for you, so not having a class that really highlights that is ... a missed opportunity.
All told, I'm not really expecting WotC to do a Summoner. I think we'll get a Psion/Mystic as the 14th class, and I'm skeptical there will be a 15th at all.