Lately, there was quite some discussion about using SDCC for MSX. There are some doubts whether the code it produces is fast enough for games. I think you´ve proven with Night Knight and your next game that it is possible to create games which look like they´ve been coded in 100% assembler.
There's a lot of ASM code in my games, but that's only for the bits that are speed sensitive. Before working on the MSX, I made games for the CPC with SDCC following the same strategy, and that machine doesn't have hardware sprites! So it is possible 
It is in my TODO list releasing few libraries I wrote to make Night Knight (and I'm improving with my current project). I hope that would help people willing to make games in C!
EDIT: also I'd like to look at this project https://github.com/KarolS/millfork
Couldn't you release that disk sooner ? 
I was just trying to give something back to the community...and i'm using a gotek drive...so size is of less importance for me ;-) But i admit, your disk is better 