I'm so glad that you picked up on the meaning of "Owen"! The "Newlin" part of it was also a play on Snape's rebirth. But whoa! I hadn't even noticed the mirror result of the name, so I definitely can't take credit for pushing the meaning even further. That's so fascinating. Thanks for sharing that with me.
I left the idea of how much Newlin remembered of Snape's life as open as I could in the story as written, but in my head I envisioned a Snape forced to relive childhood burdened with a significant remnant of his adult memories. He's still obsessed with the past more than the future, trying to understand his role in the war. Was it worth his sacrifice? Was he merely seen as a pawn by Dumbledore? Would future generations remember him as a traitor or as a hero or would they forget about him altogether? In that context, I felt like he'd see Harry's sharing of Snape's memories as a betrayal, since the memories were ones that would make Snape vulnerable. He'd immediately wonder how many other people saw those memories and be furious with Harry for so readily exposing him to a relative stranger, especially one who was writing a book and could expose Snape's inner thoughts to the world.