If enough forward-thinking is designed into the carrier, it may be entirely possible to upgrade steam cat to EM cat during a midlife overhaul.
Well, IMHO, we know from the Essex overhauls that you can do about whatever you want if you are willing to spend the time and the money...even if you did not specifically plan on the types of upgrades you ultimately make.
The question is whether this is what the Chinese want to do or not.
I personally believe that the Chinese will be happy to have their first six carriers be the following...and let them live out their lives like that, finding plenty of use for them throughout.
I believe that the last two then, will be the mold the Chinese move forward with there after.
2 x STOBAR (Liaoning Style)
2 x Conventional CATOBAR (Steam)
2 x Nuclear CATOBAR (EMAL)
Once the second nuclear CATOBAR comes on line, I expect sometime in the late 2020s, or early 2030s at the latest, they will be looking at another 15-20 years left on the LIaoning, whose replacement would them be an improved Nuclear CATOBAR carrier.
Anyhow...that's just my thinking.
Time will reveal (and in this thing long after I am dead and gone) how it will actually turn out.