There are no ‘Planes’ Not exactly. See below about ramifications:
There is no Planer Travel. In fact there are no ‘Planes’ like the ones described in base Pathfinder. There are no Angels or Demons. There are ‘power sources’, both holy, infernal and elemental and more, but there is no way to go there physically. Teleportation does still work just fine, but you don’t ‘travel’ through the astral plane, (as there is no physical astral plane), but more you syphon the energy of that ‘plane’, which once you transform people into that energy type, you can travel vast distances. In a way you are ‘in’ that plane, but not really. You may be able to mentally travel to another plane, but it’s basically aligning your thoughts so that you can precieve that type of energy rather than your mind going there. (You do this via astral projection techniques, but you don’t have a body while there… you just experience more of the concepts of that particular type of reality).
There are still religions and pantheons. People just have no proof they exist. Resurrection kinda is proof, but there are many nay-sayers.
Divination does still kinda work, but it’s more your pushing your mind to try and perscieve time from that planes perspective, rather than contacting an actual entity. (Though the spells have you ‘chatting’ with an entity, mainly so you don’t go insane trying to preceive time from time’s perspective).
Bags of holding and similar things do work, and you do ‘create’ a pocket dimension of sorts, but it’s not actually another plane persay, but more of a way to warp the physical space of our the world. Throwing a bag of holding into a portable hole is still REALLY REALLY bad. Probably worse. Don’t try it.
NOTE: Bags of holding and anything creating extra-dimentional spaces, are twice as expensive. Spells that do similar are also slightly affected, either in what they do, or in what level they are. See me about that info if you have a particular question.
All summoned creatures are actually Residium formed into a creature or entity. They all look ethereal and whispy, and don’t look real, (though sometimes illusions can be added on top to help that.) The ‘elemental or angelic’ creatures still work, but they are like the others as they don’t exist. It’s more you’ve embedded the summon with energy of that type in a specific pattern. Summons don’t have ‘intelligence’ per say, but if they have a high intelligence score they can act like an advance computer in terms of tactics and reasoning.
Unintelligent undead do NOT view summons as living, and so have a high chance of ignoring them. In combat they will ignore them unless they are attacked by it, or it’s in their way. Then it’s a maybe. (It’s not an auto agro change, as they are still far more interested in the living nearby).