Ranking up in factions is definitely planned. Full game will have eight year time limit so you will be able to become high ranking member or even leader (Only for one faction. I don't want this to be like skyrim where you can lead pretty much every faction in single playthrough).There already is a taste of this for the church. Talk to the guy in black armor who sits in front of the inn after you join the church.
New ranks for the church will teach you different kinds of magic. Not just stronger spell variations. Things like rituals or magical item creation.
INT increases your magic damage, but it doesn't influence magic from pebbles.