I'd like personally to see more exploration of the religious/spiritual mindset in SFF, because I like the ambiguity, but to be successful, I think that would have to come from writers who are sympathetic to both sides, and people tend to be one way or the other.
I agree wholeheartedly with this, and it's something that's sorely lacking in all literature IMO, not just SFF. SFF probably suffers more than most genres in this respect though, perhaps because most SFF writers and readers (in my observations) tend towards the athiestic end of the spectrum and a certain level of disdain for religions. I always reasoned that this was because most SF fans, at least, believed in "science" and a pragmatic view of the universe, leaving no room for the esoteric elements, as you describe. That science and religion are fundamentally incompatible.
Which is a shame, because it carries an assumption that these ancient practices and texts have nothing to teach, which to me just seems plain daft. My familiarity with religious/sacred texts stretches only as far as the Bible and some elements of the Koran (particularly the eschatological divinations, which are every bit as wazzo as the Christian ones), but it strikes me that the psychological truth and depth and profundity of the early Old Testament stories is staggering, and worth paying attention to.
As I've gotten older I've re-evaluated my relationship with religion. I did go through a phase of being seduced by the trendy zeal of some celebrity athiests, but I soon realised that reducing "believers" to a lumpen bunch of morons who believed in a "sky-fairy" was unsophisticated at best, and arrogant or even unhinged posturing at worst, making them little better than the zany preacher who stood outside Ealing Broadway tube station yelling passages from Deuteronomy. Now for me, the very question of "believing in God" is a very complex and multi-faceted question. And I simply think that most people nowadays want to do complex and multi-faceted. They want to pick a side and then have a Twitter war.
Some folks around here know that in my day job I work for the UK Space Agency on a programme developing space robotics and intelligent systems for orbital missions and planetary exploration. It's not Luddite stuff. And I've found that doing this sort of engineering-focused work doesn't come at the expense of sympathy or understanding of religions; just the opposite in fact. The human endeavour to discover new things, but to temper that discovery with the respect for our collective and individual histories, is a fundamental aspect of the ancient religions, going all the way back to Genesis.
Back to SFF, then. SF in particular is often about exploration of boundaries (though Fantasy also is frequently about exploration of strange lands), be it technical, geographical or inter-species, and asks questions about our role in it. These are questions posed by the very earliest of religious texts (ie leaving the garden of Eden).
The one book that has married science and religion most successfully, and attempted to rectify the growing modern disparity between the two, and explore their complex relationship was Sarah Perry's
The Essex Serpent, which blew me away, and I'd recommend to everyone. It's not strictly speaking SFF, but it does tend towards the speculative, and particularly the phenomenological gaps at the edge of our knowledge, which we fill with scientific endeavour and religious reason.
For my part, I've wanted to explore the potential conflicts and reconciliations between science and religion in my a novel which I've parked for now, as it requires more intense research and immersion than I'm able to give it right now. In my WIP the characters frequently meet in a ruined, hollowed-out church, which is symbolic in a Miltonesque way (ie the abandonment of the divine in favour of one's own intellectual self-worship, which is posited in
Paradise Lost as Lucifer, the most fantastic of the angels but falls, as he is intellect decoupled from God), and it does explore themes of creation and freedom, which are both intrinstic to many religious lines of thought, but taking on this big stuff is difficult, and scary.
TL: DR - Science snd religion often seen as adversarial, or opposing forces, but there are deeper psychological truths that apply to both, and therein lies the possibility of exploring reconciliation.