Personally, I think a god who used to be another god and has since passed on that mantle would be very interesting. An old grizzled god of war who no longer fights in battles but remembers the glory and horror of combat. He might be worshipped by veterans or even the families of soldiers who wish for their safety and survival. A reformed god of drink who has vowed to never deal with alcohol again because he has seen what abusing it did to some of his followers. He could be worshipped by anyone fighting addiction or wishing strength to loved ones who are. A retired god of adventurers who has become benevolent and calm in his (relatively) old age, and whose worshippers run museums full of ancient treasures brought there by explorers. More of a silly suggestion, but what about a god who spends their time judging which objects and concepts are worthy of having a god? This god's opinion could bring into question the validity of Caseus, god of cheese, because Bos, god of cows, already covers that. At the same time he could help end debate over whether or not Pileus, god of hats, deserves recognition alongside any other god of clothing.