Alternatives - Transcendent or immanent?
Yet another binary...
Not sure I grasp your question. It isn't an "either/or" dichotomy. Orwell was demonstrating a political philosophy. Rand's philosophy was in opposition to that political philosophy, but wasn't a political philosophy of itself. It was more of a personal liberating philosophy, only because I am hard pressed to define it. She was an atheist if I recall, so I can't call it a religion, and of course it didn't have a religious text. It was how she felt someone should guide and direct their life. In that sense it was really no different than Stoicism. The Romans and I think the Greeks supplemented their religions with Stoicism, particularly among the ruling classes, but by itself Stoicism was really just a practical outlook on life. One could easily be a Stoic and an atheist - today- without any conflict. Objectivism is a lot like that.
I was just thinking a few moments ago about the amalgam China has put together, merging in their own unique way both Communism and Capitalism. I know just enough to get into trouble and can't offer any specifics, but it seems to me that among their entrepreneur class there are people that demonstrate tendencies very much like Objectivism...how's that for a combination? I think Rand would turn in her grave.
Another way of considering the whole subject would be to think of these philosophies very much like memes. I know Dawkins trots it out like a meme is a bad thing, but he fails to note the very meme he uses. Memes are simply internal dialogue people use to direct their decisions. Most arguably have some basis in one or another religion, but depending on life experiences and education that may expand well beyond the borders of a particular faith, and we see examples of people holding to tenets and beliefs from various faiths and philosophies, and use various mental gymnastics to juggle them around into some coherent workable solution, at least for them. I get a tickle sometimes watching these patchwork philosophies go at each other, it can present a good bit of comic relief, because they presume each understands the other but they are talking past each other, and neither can keep up!
I don't know that I answered your question. To me, personally, it is a very fine, fuzzy line (sometimes) between religion and philosophy, probably the only distinction being that philosophy on the whole doesn't get carried away with texts...some philosophies can be written on a single page. Can't really say age, there are ancient philosophies, but most of those have either fallen to the side or been merged (effectively) into something more modern. Utilitarianism, in my opinion, seems to pick up where Stoicism left off, for example. Religion generally takes itself pretty seriously, philosophy generally seems to have a "don't care" attitude - you either do or don't, no damning to hell. But both supplement the meme inside our heads. The exception would be political philosophy, where if you don't agree with the ruling philosophy it might get pretty unpleasant.