You want to propose other natures without causes? Then if they always existed man would not still be sinning to the extent he still does. The composites of the universe all require a cause, for whatever begins to exist needs a cause (Kalam's).
Lots of atheists believe things like radioactive decay, particle pairing, Bell's Theorem and vacuuming (fancy phrases they throw around) come from nothing yet they can never actually prove it. So understand this is an approach you can easily slip into, especially when you previously argued the universe had a beginning but was not created. How is this possible if there is not an eternity of past, which is itself impossible?Of course. I'm not suggesting that something came from nothing. If you want to know what I believe, I'd say that everything was packed into a nearly infinitely dense point. "Before" that, I don't know what happened. It's difficult to say "before", though, as time didn't exist before space.
When you say you "don't know what happened" that's shutting your mind down to the evidence we have already discussed. What happened before singularity was the uncreated created and intelligently designed since singularity, being nature, requires a cause, and there cannot be an eternity of the past of cause and effects, for man would not still be sinning.