As far as actual armor, there’s only a few pieces I think would have actual clipping issues on them.
Cloaks/Back pieces
2H weapons that are sheathed on the back.
Everything else could easily fit them. Even helmets. We have Worgen and Tauren out here warping metal to fit their odd shaped heads, Dracthyr could too.
Dracthyr could wear armor. It’s very possible if blizzard wanted to take the time to fit it to them.
Most of the pieces would be easy I would think. Gloves, boots, pants and chest would be pretty straight forward. The only piece I think might be tricky is the helm, but I think it’s very doable
Not only that but when they were being used by Neltharion against the primalists, he was also developing weapons and armor for dragons and dracthyr alike. He had an entire arsenal stockpiled.
The issue is that the developers cut corners when they made the Dracthyr, because allowing them to actually wear armor would actually require them to put in the work to retroactively make all older armor pieces fit for their bodies.
Or time/cost constraints. Practicality isn’t evil, either.
The dracthyr model is unique. We have 2 decades worth of gear that needs to be updated to fit them.
Good news, though, they’re working on an AI driven solution to automatically adjust the gear when they create a new model.