Unfinished, but not a total loss
Unfortunately I won't finish my Ludum Dare game in time, but progress was made on the game this whole weekend.
Here's a screen of the ROM running in BGB (a high-accuracy GB emulator with good debugging tools!)

Since I dunno how well the image upload handles large GIFs (this one is 7MB), here's a Twitter link, showing a capture of the engine so far in action.
https://twitter.com/eggboycolor/status/1122593568357482496
I implemented a text box system. There's horizontal parallax scrolling with table-driven system to allow an arbitrary number of scanline splits. There's state switching / swappable update handlers. I glued together a bunch of systems to enable writing this game. Just burned too much time doing the setup.
I think there's simply too many systems that go into an RPG (even a light one) for it to be a single weekend project once it's being written in asm. I think the scope and general plan for this project is achievable, just not in such a limited timeframe of 48h.
It was a good way to exercise the tools I wrote though, and organize more things for future homebrew development.
I think I'll keep the idea alive. I'll try and release something following the original game design. Until next Ludum Dare!
You can follow along on @eggboycolor on Twitter.