Normally in the development of Iguana and Chameleon we go out of our way to try and preserve backward compatibility. No one enjoys upgrading interfaces. The Translator on the other hand is a complete re-think of our mapping technology.
With completely different APIs there was no benefit in staying with the Python scripting language used in Chameleon.
It made more sense to pick the best language available for the Translator.
Will all my Chameleon based vmd mapping files still work in Iguana 5.5, i.e. is vmd backwards compatible?
Absolutely 100% positively yes.