Well, I've been looking for a four legged dragon for a while so I know that adding two real and fully animated arms would be really hard, and i'm not really complaining about it since i'm just a random player who doesn't know shit about modding
though, just adding two small (non animated) arms, kind of like a T-rex, would be fine with me, this way there should be no animation problems, Also, a dragon with small arms walking with his wings wouldn't be too weird i think, if they are well placed on the body, with the right size, i think it would still be pretty cool
also, for the elder scrolls univere, i know that those are considered dragons, well wyverns are a sub spiecies of dragons anyway. Though, i know other forms of dragons exist in TES universe, for exemple, Peryite's dragon form is a four legged dragon, and i'm prety sure i've read some book in skyrim about a sea dragon somewhere....
I think bethesda should've add some more diversity to the dragons in skyrim (durnevir would be great as a lindworm, and Alduin and paarturnax would be cool too as the only four legged dragons in the game, since they are more "unique" than all the other random dragons...) But, well, that's not sur topic here so I'll stop talking about other dragon species
again, you did a good job with your mod
Edit : oh, and sorry if i made any mistakes in english, it's not my native language