If you told me any of the holoEN girls were younger than 20 I would be shocked. I think Haachama is actually young but otherwise I imagine everyone on holoJP is actually 20+ as well. (Just personal reads, not based on anything but my own opinions, and I don't know a lot about a lot of the JP...
I'd love to see "redemption arcs" for all the main protagonists. Where they fix their shitty ways, and Melissa doesn't get with them but they at least understand the ways in which they've been shitty.
I saw the "normal" ending from the beginning; it was a good use of a science concept to tell a sci-fi story. The final bit of the ending was kinda weird, it seems strange to me that relativity would go out the window given how rooted in relativity the story is.