Some more speculation about Jangmo-o...
Stopped by Bulbapedia to see what was posted there and it seems it's name is based off of 'jangling' which is a metallic jingling noise, most likely in reference to it's scales possibly clinging against each other...It's Japanese name Jarako is also based off of jarajara which is also the sound of jingling (ko from Draco or from the Japanese Ko being Child or young one)...jjang (Korean slang for 'best' 'top' or 'super') is still possible depending on what it'll evolve into, though it does seem a rather obscure reference in comparison especially since it's a slang word...it's like naming a pokemon after "Too OP PLz Nerf"...of course I wouldn't hold it against Game Freak as they have come up with some weird names *looks at Type: Null*
However it's Korean name is Jjarangkko...though it is similar to the Japanese name with similar etymologies...it's interesting to note also...
Couple the jangling reference with it's soundproof ability it seems likely we may have another sound-based dragon of some kind, from the sounds of it this one's likely themed around percussion bases sounds as opposed to the sonic screeching noises made by Noivern and it's subwoofer ears...
This could possibly give it access to moves like Metal Sound, Screech, and possibly Uproar? Perhaps even a new sound based move...perhaps something centered around rattling as if it rattles it's scales...
This doesn't support my Griffon theory though it doesn't debunk it either...it's definitely a gimmick I can see a Griffin pokemon use especially if it gets scaly armour and perhaps skarmory like wings or something...If there's a focus on the metallic sounds and armour it could also lead to a potential Steel typing, though I'm still leaning towards this guy becoming a Fighting type...
Also had a thought it could possibly be called 'Jangriff' if it does indeed evolve into a Griffon...seems rather simple compared to Jangmo-o...but then again 'Goodra' isn't the most complex name for a final stage psuedo so...