As you can see from this video by RenaKunisaki, work on the Krystal mod of Star Fox Adventures continues very quickly. As of now, I believe Krystal is playable in all areas of the game, with some minor hiccups. This is actually using Krystal's game object, not replacing Fox's model with Krystal's. As a result, Krystal keeps her sound effects where they exist. As of now, there are still some visual glitches, such as Krystal being too tall for some areas due to the slight difference in height between her and Fox, as well as lack of animations for parts of her and some things she was never intended to do. We'll see how much those can be improved in the future. Replacement of voice samples and sound effects might be relatively straight-forward.

You can find the full Gecko code to do this yourself (with your legitimately ripped, personal copy of Star Fox Adventures!) in the video description. Additional codes, information, and tools can be found at the Github project page. In case you were wondering, the audio desync issues are related to the video editing process, not because of the mod.

Research and continued work are discussed on the Krystal Archive Discord. For instance, they've figured out how to spawn almost any object they want. Check out this picture by Nightcast!