You are way, WAY oversimplifying the development process if you think that having ability concepts is the hard part of class design. That part is the easy part. Anybody on the forums could spend 5 minutes and come up with ability designs for a class; the hard part is implementing them and writing it into the story.
The only reason I'm opposed to Necromancers is because I would rather see the development team's time and efforts go into something either new and fresh for an MMO (like Mathematician) or something very iconic and with a playstyle we don't really have (like Thief or Ninja.) We're already getting a pet class with a wide variety of spells with Arcanist and Summoner, there's no reason to start clamoring for a second one right now.
So you want two pet classes immediately released one after another that are both going to be hybrid spellcasters? That seems like a giant waste of time and it would be insanely hard to make them diverse enough to be noticeable.