I think you're overlooking the no coin no reset. I mean, Idriel is flipping the coin throughout the game and keeps bringing it up so we know it's an object she has, and it's unrelated to how people can come back if their astral projection dies. It'd be an oddly specific thing to say if it was meant more as a metaphor for second chances. There's something she can do in Eternum that's saved Orion's ass before, but can't do that in real life, or how that's how interpret it.
The full line was "there is no coin HERE. No reset." I thought that HERE meant real life, hence my interpretation as to what she meant.
All we know about the Limbo is that it's Idriel's prison.
Also the lines were "because we've seen it. Because we've tried." You could interpret that as them witnessing the event in person, but the Limbo infodump implies that they could be viewing things from there and projecting themselves into Eternum just as how Idriel does when she projects herself into the Nexus (she does mention that outside of Limbo she's basically a "hollow shell.")
You mentioned Orion not remembering his dreams, which is brought up half a dozen times in the game. I always thought it's weird because he seems to remember it immediately after it happened (like feeling his neck when he was chained), but then never thinks of them again and seems to believe the next dream is always a first. It's definitely a clue for something. His headaches when something important is happening. Idriel wanting him to remember. His dance with Penny and feeling like he learned to dance in another life.
It all points to a lot having happened in the past, and there's only so much that could've happened in a 18 year old's life. If you ask me, there either has to be a loop (maybe even during the game we don't know about) or he's lived multiple lives.
One of the issues with the loop theory is that it implies Idriel and the Syndicate have no fucking clue what they're doing to rectify the issue of being in a loop. On one hand, their support basically implies that they're laying down the path Orion needs to follow in order to help him with the gem hunt and ultimately break the loop. But then there's Idriel conditioning Orion to always choose differently even when things are inevitable with the heads or tails talk. Then when Orion gets shot in the alley, she tells him that "this was not foreseen" as if that was a bad thing and that his fate in that alley is the end instead of reminding him about the heads or tails talk (which would've clued him in and made him want to live and thus made the discovery and use of the new ability all the more natural). And then there's the Valley of Kings guy being astonished that Orion doing something NOT inevitable...as if they weren't trying to pave the path to him breaking shit in the first place.
Another issue with Orion being in a loop is that usually at this point he should start feeling a sense of deja vu that grows stronger as the story nears its climax. We have tentatively 5 chapters left and Orion still doesn't have that feeling except that one time with Penny (which one could also possibly construe as him having some sort of prescience like Idriel and the Syndicate but since he forgets his dreams the only thing lingering is in the subconscious). Multiple lives may work but there's nothing in the story other than that throwaway line in Penny's Ekabar path that foreshadows that (unlike Orion's new ability which tracks since it feels like a natural evolution to Orion projecting himself in Eternum without the headset and also answers the question why the Founder hasn't been seen in real life and is only seen in Eternum).