In the same way that a small terrier and great dane have both been engineered from the standard 'Dog' what are the limitations on supersizing a Komodo Dragon?

Weight and heat production increase as the cube of relatvie size increase, weight-bearing and cooling increase as its square. Compare the skeletons and metabolisms of a mouse and an elephant.

Why would you want a 20 tonne Komodo Dragon (imagine mucking the stalls) when you could make your fortune growing fangs on a goldfish?