So the two systems are completely different. Classic steam cats use the steam generated by the propulsion plant to pressurize the catapults and propel planes off the carrier. EMALS uses the steam generated by the propulsion plant to generate electricity to launch planes similar to a railgun (as I understand it; might be wrong but the core concept is there). You can’t really have both, and retrofitting is costly and expensive, because now you need to be able to transport the steam to the right place, be able to contain the steam, etc. and that is not to mention any issues with whether or not the propulsion plant can produce the steam required to operate the cats. I have a hunch electricity generation is more efficient from a steam use perspective than steam cats.