By all metal I mean the whole corpus of the instrument in metal(s), like the French clavietta or accordinas.
The melodica-type music instruments of the 19th century were wood or metal instruments.
The 20th century melodicas are plastic. Don’t the melodica players want metal ones ?
Plastic is lightweight, but the sound isn’t great. A plastic melodica sounds harsh/sharp. And most melodica reed plates are low quality, with air losses.
Top quality melodicas could help upgrading the status of the melodica in the music instruments family.
The vibrandoneons, seraphones, and the likes are fine top quality instruments, just a bit heavy.