Didn't work for Sonic unfortunately.
Over the past week, I've come up with a theory as to what's going on. Hypothetically, you should be able to export a model from the game and reimport it perfectly since you're not changing anything. So then, why do we have missing meshes, misappropriated textures, and characters that don't load? I'm guessing that there's something fucky going on with Ohana's MBN export. When reimported, Mario's textures are offset, Toon Link's rigging is "close" but not perfect, and I'm guessing errors in exported rigs causes characters like Sonic and Wii Fit Trainer to not load by default.
Smash Forge has some WIP MBN stuff on the github, so hopefully one day we'll see that fully implemented. Again, this is all just a guess as to what's going on, please correct me if I'm wrong.