Any D-30 skin should be placed on a D-25 model.  The presence of a dorsal fillet is not, IMO, more important than the higher performance of the D-40 with the later engine.  For almost all of the characteristics we care about in-game, a D-25 = D-30.
Now, if we have D-40 skins that are D-30s, I'd take exception.  That being said, ultimately, its HTC's call, so contact them and see what they say.