I've always had a soft spot for the summoner class. But it stems largely from a deep appreciation for the Bartimaeus trilogy by Jonathan Stroud. Like the summoner, Bartimaean magicians had several minor magical tricks they could perform without needing help from an outsider, but their most powerful abilities by far came from their capacity to command spirits/demons from the Other Place. Skilled magicians could conjure weaker spirits with a snap of the fingers and a few words, but their greatest strength came from spirits/demons that could only be called and controlled with the help of complicated magical diagrams and rituals. A magician's power was most directly measured by the strength of spirit/demon they could call and subsequently control.
If I didn't know that the game was drawing on preexisting traditions, I'd swear the author played D&D or something.
There are a few key differences, though. Namely, a summoner in the Bartimaean mold would have no eidolon. Mostly because, save the rare few who develop Stockholm syndrome, every bound outsider is like the quasit: "[It] serves, yet it watches and waits for mistakes that might cost its master's life, or even better, an error that might let the [spirit] turn against its master."
Also, Bartimaean magicians bargain and negotiate purely with sticks. They never give their slaves gold, goods, or services, and instead rely on the strictures of the binding magic and their ability to magically torture them into compliance. The idea of having a spiritual connection to their slaves beyond that necessary to ensure their compliance would be anathema.
Of course, the Pathfinder summoner derives a great deal of their power from the eidolon, so removing it would change the class significantly.
Does anyone have any ideas on how to implement such an adjustment?