In the Core Rules of the revised IKRPG, infernals are mentioned twice (pages 35 and 96) and infernalism is mentioned once (page 85). The information on infernals/infernalism combined takes up less than a page and pretty much leaves almost everything up to the imagination.
In fact, most of the information on infernals actually focuses on the possible connections to the Thamarite faith rather than the infernals themselves. There's no mention of what domains infernals typically control (such as teleportation effects as in the original RPG), and only a vague connection of infernals, Thamar, The Vanished (6 out of 8 Iosan deities are missing), and human magic.
The only real concrete information we're given is that infernals are "mysterious but vastly powerful entities that dwell beyond Caen and Urcaen" who gather mortal souls for unknown purposes. They are said to be highly skilled in arcane arts, to the extent that it is believed the Orgoth's dark gods may have been exceptionally powerful infernals.
I'm not too sure how this differs to the older content on infernals, other than restrictions on most teleportation unless bargained for with an Infernal of the appropriate (but unknown) stature. In addition, I don't know how to resolve differences between the content of the new RPG and the old one. So, I feel that this answer is still incomplete.