I've always conceived of warlock pacts in Forgotten Realms (if not generally in D&D post-4E) as being connected to the plane. In essence, the warlock draws raw power from the plane itself, throught a magical connection provided by or embodied by the pact's master, a being from that plane. So Farideh draws powers from the Nine Hells through a connection Lorcan manages, Japheth draws powers from the Feywild through the Lord of Bats, and Andareunarthex draws powers from the Far Realm through teh entity Sualocin, etc.
This morning it occurred to me that such an arrangement might also be made through someone on the Prime Material. What if there are beings on other planes who use whatever it is that powers the Prime Material Planes (like Toril or Oerth or Eberron) to fuel their magic? Who would make a good PMP pact master? Is this the purview of wizards? Or maybe someone more tied to the land and the plane--morally flexible druids or priests? Kings or queens?
I don't know if this will ever be something that comes together tightly enough to use. But it's definitely piquing my interest this morning.