Based on his quotes and the world he created, he doesn't seem someone whose worldview is based on Ti, he seems more value-based than reason. At the same, he colud have seem a Si-Fi kind of ISTJ, with Fi values giving support to Si impressions. Now take George RR Martin, he loves Tolkien for the details of his world-building (Si) but he thinks Tolkien didn't deal with the implications of his world (Ne or Ti): what if a good king is not a good ruler? what happens with the baby orcs? If you compare the two, it's clear Tolkien couldn't have been an INTP. At the same time, yeah, he couldn't have been an INFP. INFP doesn't mean one is good at characters, but they have a need to exorcise their own internal cinflicts in a story, deal with moral conflicts or moral nuances, which Tolkien lacks in favor of the simple white vs black.Tolkien... has an enormous amount of Si. I actually think he's ISTJ, but I've seen good arguments for INTP. (Not sure he's INTP, though -- he got into some hissy fits with Lewis about blending fantasy and the real world by crossing over elements, which might hint at SiNe instead of NeSi with a Te function involved.)
So, for an INFP we need a fantasy author getting different moral dillemas that follow from a story, or at least one with a genuine sense of tragism. Anybody like that?