SinoSoldier
Colonel
I'd rather prefer that the Chinese use both J-21s and J-20s on their carrriers. You want a high-end air superiority fighter on your carrier as well as a strike fighter, which is what the J-21 is going to be. The news about the sensor suite upgrade is very promising; there is no reason the J-21 should omit EODAS except for cost.
Logistical issues may pose a problem with this plan; you would need spare parts, engines, and weaponry for aircraft in two different weight classes, although it could be done if necessary.
Whichever aircraft is ultimately selected, hopefully China's carrier-borne fighter mix over the next 15 years will be weighed heavily towards the fifth generation. As the carrier program is just getting started, there are no previous-generation fighters to replace. Is there anything the J-15 does better than the "J-XY"?
Seeing from the lack of progress on the J-15T technology demonstrator, I'm willing to bet that the Chinese will go from an all-5th-generation fleet from the get-go.