If you had a fully animated and exported dragon model, you could copy the hydralisk, rename the datablocks, change the model, and change the projectile(s) and you would be done.
But the greatest barrier (and really, the only one) is the model. Get a model, and any decent scripter will probably be able to make it work. (Likely by copying the AI of the hydralisk, but some people might instead write their own.) Although, finding someone who wants to do work for nothing will aldo be a challenge...
