Allowing you to keep your warforged feats should be interesting, as IIRC you could get yourself immunity to non-lethal damage, +AC, a bite attack(scales with size), a slam(scales with size), and spikes that act similar to armor spikes dealing damage in a grapple. I realise this is by no means the most abusive thing a druid could do, but at the very least the idea of a giant metal animal covered in spikes charging at the enemy is fun to picture.