What a great research topic! You probably already know of Eugen Doga and of Japanese composers such as Nakoto Namura who use the melodica in composition. Also the great Brazillian composer whose name slips my mind, the one who sparred with Miles Davis. (I’m not where I can search without aborting my post!)
There have been some posts here, especially by Jazzman1945, about the value of the melodica for learning improvisation. That was one of my reasons for taking up the melodica.
You might find it useful to pose a few questions here for general conversation, so people with relevant knowledge and expertise can jump in.