This was supposed to be more like a reminder than anything, but anyway I'll share my thought.
I often think about ways to make multi-layered maps. Not only mean to graphical layers, but, like, a map with different elevations.
For my RMXP game for example, what I did was the same I did in RM2k3 back in the time I used that (now I own it because I still love it). Changing tilesets on the fly whenever the character passes by a certain place. The thing is that this both works and doesn't. It works for the player, but events get screwed, so I can't put roaming NPCs since they not only get stuck but also display wrongly if a tile above them changes its priority so it shows under them. Instant teleportation (?).
So I was thinking about it, and then I thought, what if I merge two maps? I could display two tilemaps at the same time, one for each elevation level, then make the player transfer itself between one and the other level. It's displaying and running two maps at once, one above the other. It should be possible, but the performance will take a huuuuuuge punch in the face.
Another way would be to display them both, yeah, but managing them as one, so when the player goes up a level, what changes is the set of passabilities it takes into account (there are passabilities for each level). then I give it a Z offset so it displays correctly over the tiles it should. Thing is, I would need a lot of time to plan ahead these maps. But seems doable! Pretty much all I need is to make the logic part and remake these maps.
But all this is going to the thoughts pot, since I can't delay this game anymore. Maybe for a next one? That's why I wanted to make this thing, to leave this stuff here and look at it later. So, laterer me!