One thing I've been noticing in the guide is that there's a few henotheistic Orlanth/Malkioni hybrid cults around. You've got
Invisible Orlanth in Carmania, which claim Orlanth was enlightened and conquered the Invisible God, probably taking over some of it's domain judging from the name.
Aeolianism, where the Lightbringers are intermediaries to the Invisible God
The Chariot of Lightning in Ralios, where Orlanth is the Supreme God (the guide doesn't say the Invisible God but the description seems to equate the two).
There isn't really a connecting thread aside from the gods involved and how recently they popped up, but I don't really see an equivalent for any of the other pantheons. Other gods, like maybe Yelm, Ernalda, the Red Moon, or Arachne Solara, feel like a better fit, but I haven't seen anything along those lines. My first reaction is that most of these are down to political reasons where it's a justification for cross-cultural integration, but that's not particularly satisfying and doesn't explain why it's always Orlanth. It might be because they're both fairly flexible in their worship; there's a lot of different approaches to Orlanth and the I.G. and the latter doesn't manifests so you can really say whatever you want. Are they onto something, or is it down to more mundane reasons?