*raises hand* Do Catholics count as Christians today?
I don't read or write C-fic because my worlds start at the edge of ours. I read and write almost exclusively specfic. If I read contemporary, it's going to be because it teaches me something new about the human experience, much the reason I read nonfiction when I read it. Especially given the sanitized version of humanity it seems C-fic goes for, I'm not likely to pick it up.
I do, however, have something of an ongoing couple projects that are... not Christian fantasy, but certainly fantasy whose driving force is the Christian cosmos, with all that that entails. I've got a fantastical mystery about archangels and prophets, and somewhere on my drive I have one where I redeemed Lucifer. Because way back when, someone let slip that in Islam and in Christian occult theory, Lucifer fell because he wouldn't bow to humans. And this spawned all KINDS of plot bunnies in my head.
Also, regarding cursing: I cuss people out on a fairly regular basis, but I try not to even let my friends say g**damn or use Jesus's name as an expletive around me. I still say "oh my gosh" and I'm 26. It makes me quite uncomfortable otherwise. My mom instilled that in me as a child, not by emphasizing that it's "bad," but by asking how I'd feel if someone used MY name like that. (It also didn't help when I read Hammered, third book in the Iron Druid Chronicles, and Jesus mentioned that he routinely heard people saying his name during sex. That... yeah, that convinced me.)
Other dimensions and/or other worlds certainly carry theological implications, and I don't see why in certain circumstances Chrisitan theology and ethos, or even the faith itself cannot bleed over. I cannot speak in detail to varying schools Protestant soteriology or eschatology, but the Orthodox theological gnosisphere offers a lot of territory to explore in literature. The visions and experiences of the Desert Fathers are very rich veins to mine if done respectfully. Foundational to Orthodox soteriology is the idea that Christ to redeem not just man, but the whole of creation...that provides huge scope. Corrolary to that is the idea that salvation has much less to do with getting to heaven, than becoming heaven. All creation exists to be fulfilled as an event of communion. Or to put it more mundanely...and too simply is that creation is meant to be both a vessel of and communicator of the Divine...like a wet sponge communicates water with but a touch or a red-hot iron pulled from the burning coals communicate fire to whatever it touches. Theology, genuine theology, not the stuff learned in classrooms and read from books, is experiential. It is honey tasting from the comb...an experience no paper on honey chemistry will ever communicate, nor is able to communicate.
You mentioned a story about a repentant angel, Lucifer, I think. Consider the implications embodied in that conceit. How does a fallen angel repent, especially the worst of the lot? If angels can repent, why haven't any...or have there been any? If they can't what prevents them? How can that obstacle be overcome, if it can be overcome? Some insight can be gained from the Book of Enoch, which has an extensive section on the nefellim, fallen angels and the degrees of their fall. Some are in a much worse state than others.
Patristic Orthodox theology teaches that angels can't repent because that are non corporial. They have no flesh as we do, and not weakened in their intellect and natives powers as is man who is very changeable. We can repent because our nature permits us to change, even back and forth. Angels have a will that once directed in change is fixed in that decision. They are not mortal and are not able or willing of their own accord to redirect their eyes, so to speak.
So with that in mind here is an angel/demon story from the time of the desert fathers (I believe) that shows a little of the places one can go.
Once there was an old monk, a holy man who lived alone in his cell in the desert. His life was a constant struggle of prayer and repentance, and because he had made so much progress, and had remained steadfast in it so long, a devil came to torment him, and did so from many years. It suggested lewd things. It tried to insinuate laxity, or dispair. It even tried to infuriate him at prayer by knocking off his hat.
Finally after one particularily disruptive night where the devil knocked off his hat again and again, the monk turned to the devil and made the sign of the cross fixing it in place. The devil could not move, neither to trouble the monk or to leave his little hut. The monk returned to his prayers but soon enough was disturbed by the shrieks and wails of the devil. It said the prayers burn him terribly and he could not bear to hear them and begged to be released. The monk continued to pray, and the devil wailed and cried out all them more. It promised to leave and never to return if the monk would just have mercy and free him. The monk thought for a moment and then said that he would release the devil on one condition. Eagarly the devil agreed, anything to be free.
The monk then made his demand, that the devil should sing the song of creation that all the sons of God (the angels) had sung at the dawn of creation before the fall. The devil said he could not remember, so the monk continued to prayer and let the devil scream and cry a good while before he regarded it again. This time the devil said it was impossible because even if he remembered the song, there was no way the monk, who was of mortal flesh could hear it and live. Once more the monk returned to his prayers.
Finally the devil cried, "Enough. I yield," and began to sing. At first, his voice was raw and hoarse and horrible to hear. It croaked, and stuttered, and growled and quavered, but gradually became clearer, and more fluid, less harsh, and-and the evening hurried into the wee hours of morning the song had grown majestic and beautiful and splendid beyond all words to tell. When the sun broke and its golden ray showed through the tiny window of the little hut it illumined the old monk who now lied dead upon the floor, his face serene and blissful. And over him stood a great and glorious angel whose wings spread wide and whose voice poured forth the bright celestial hymn no mortal ear can hear and live.