Ah! Neat, I see now, so you’re hooking up the tiny-lisp runtime to a graphical front-end! 
At least replacing SDL is not too difficult, the SDL bindings(not the font stuff or audio stuff) are pretty standard, they’re comparable to X11, wayland and HTML5 canvas enough that porting from one to the next, if your code is just 5k it won’t be too much work I think(hopefully you never have to).
I’m excited to see what you make with that. I feel like the thread took a Collapse Computing turn.
Recently I was helping someone add SVG support to their project, and I just could NOT believe how large the codebase was, looking at that massive archive gave me vertigo more than any other project I’ve come across in the past. It made me wonder if this could ever be rewritten from the ground up, if it’s even human feasible.