First off, I enjoyed the game. I think it looks great and the atmosphere is great and all, but why are you all trying to figure out the meaning after:
He isn't interested in telling a story. He wants to bamboozle us. "Fewer clues, more obfuscation!"
Fuck that.
Why not try to tell a good story? Isn't that the point of writing?
So whenever I felt there was something of interest in INSIDE, rather than trying to figure out what it means, just imagine he is chuckling over some obscure piece of bullshit he put in just to confuse you.
I am pretty sure the process went like this:
"How shall we end it?"
"Just have it at the beach there!"
"Why?"
"It'll keep them guessing!"
"But why? What does it mean?"
"Nothing, but it'll keep them guessing haha"
Life's too short for that shit.
Good luck with your theories but even the creator himself isn't interested in giving you a coherent story, so why even try?