I just thought of something interesting.
While Hometown is clearly a cage of some sort, I think it's only been like that recently, and the original Hometown wasn't.
Maybe this can all be tied back to the alternate timeline theory, but doesn't anybody else think it's curious that the internet, a link to the outside world, has just been down for days? Asriel, who exists outside of Hometown and was meant to be showing up for the Festival doesn't?
I think that the experiment of Deltarune may be somebody taking a copy of the town and keeping it separated from the rest of the world during the experiment. (Possibly with the idea of using Susie to mess with the prophecy?)
The Shadow Crystal may be showing Hometown outside of the experiment. Which explains a LOT.
-You thought you saw Susie glaring at you, coldly...
-You thought you saw Noelle close against you, whispering.
We've already been through these Noelle and Susie ones enough, but where the experiment theory really starts to shine is:
-You thought you saw your mother holding someone else.
This would be on Festival day. The day Asriel was probably meant to be home.
There's also the unused text for Chapter 3:
-For some strange reason, for just a brief moment...
-You thought you saw Undyne frozen in ice.
Which, if Noelle were there, and the Knight didn't kidnap Undyne, might've been required.
It's not so much an alternative timeline, but a captured bubble of space.
The Shadow Crystal when used in Dark Worlds tend to allow you to actually see the world outside of the Dark Worlds, too. (So it's possible that the Noelle holding flowers scene was actually taking place inside of Flower King and not the Dark World made within it)
Now, if this does turn out to be true, then it means that escaping from Hometown won't put Kris and Noelle in some backrooms grayscale hellhole, but the original Hometown. The big question is whether it makes them duplicates, or if it puts em into their other bodies, or if it turns Kris and Noelle into Goners or someshit.