While we're talking about religions, I want to propose so that the Valyrian religion is made on the image of vanilla's pagan religions, let me explain; the Valyrian belief system, much like most other pagan religions in vanilla CK2, is a religion tied to the ethnicity of it's people, and because this it is weak against the more proselytizing religions, like the FotS ( early Christianity) and R'hllor (Zoroastrianism, though it takes some elements from both Islam and Catholicism), also, I guess that most of the former Valyrian colonies only converted to Rhllor worship (and some didn't at all, see Braavos for example) only many years after the Doom. I propose an alternate history situation for Aegon (or any other Valyrian religion king strong enough) whereby he decides to, instead converting to the Seven or keeping the (unreformed) Valyrian faith, reforms the faith, noting the influence the High Septon and the Seven priesthood have in Westeros. He restructures the faith with a similar hierarchy to that of FotS religion, and has this new priesthood take a more active role in converting and expanding the new Valyrian religion, so that he's not influenced by the Seven's priesthood and doesn't have take into account the wishes of the High Septon.