I decided to take a small break from networking to add a different feature. I thought I'd post it here to ask the community what they think. In fact, I am totally cool with pull requesting this into vanilla NXEngine-Evo, if you'd like.
It co-exists with the standard sprites, rather using its own .sif file and reading the files from .bmp rather than .pbm. And, of course, it can be easily redistributed without the actual Cave Story+ files, just requiring a user to copy the data/base folder over from CS+