According to the latest (or one of the latest) paid 察话会Au podcast by the Guancha Trios (which, unfortunately, I have no access to - Courtesy of @vincent for the news), particularly from Yankee:
1. China is indeed building two proper aircraft carriers simultaneously right now (not including the currently-under-sea-trials CV-18 Fujian);
2. One carrier is conventionally-powered (presumably CV-19), while the other is nuclear-powered (presumably CVN-20); and
3. The nuclear-powered carrier will be much bigger in order to accommodate the operations of future 6th-gen carrier-based fighters (presumably naval variant of the J-XDS).
(Phrases of my own are in Italic)
If this is confirmed I would suspect that CV-19 will be a sister ship to CV-18. This would allow for the carriers to be separated by fleet: CV-16 and CV-17 likely in North Sea and CV-18 and CV-19 in South Sea. With two ships in rotation one is always in readiness (aka: two is one, one is none) and similarity in class will be beneficial for maintaining crew readiness and streamlining training.
It would also match the four 055 in each fleet. Two carriers each with two cruisers
I don't think putting one CATOBAR and one STOBAR carrier in each fleet makes any sense. Despite common roots they are not comparable tactically. I also don't think North Sea Fleet needs a full carrier. Right now it would be wasted on that theater.
BTW I don't know how reliable Chinese Wiki is but Eastern Sea Fleet has Sichuan (076) listed along with two 075. No carriers for that fleet is practical for as long as eastern shore of Taiwan is not under PLA control.
As for the CVN-20 - Much bigger relative to Fujian or Ford? I don't think we can know for sure, for the time being...
"Much bigger" can be used only in comparison with Fujian. It is not rational to expect that it would be significantly larger than Ford which already approaches practical limits for this class of ships. Fujian has 316m deck while Ford has 333m. Full displacement is (speculative) 85 000t to 100 000t. Ford is therefore 20% larger in terms of displacement and 5% larger in terms of deck length. This is a similar change in size as between Fujian and Shandong. I think that would be more than enough.
CV-18 Fujian is by no means a perfect design - In fact, still some distances away.
That's putting it lightly when you consider that a supercarrier is currently the default design for any high-tempo operations. Fujian is barely making the cut there. It's the "we do not grant you the rank of master" type of admission to the supercarrier council.
The most important element is the catapult because this allows the use of full payloads. So unlike Liaoning and Shandong the fixed wing element will be fully utilised. But that is it.
The true value of Fujian lies in it being the first carrier fully designed and built in China.
Some of the advancements should include the following (or perhaps a wishlist):
The most crucial advancement is building Fujian without all the errors that Fujian has
It's rarely discussed due to the political nature of military procurement, but naval shipbuilding is very much like civil engineering, in that the "final" design reveals so many problems during construction that the resulting design may as well be a different ship. Personally I enjoy hearing those stories because they are fascinating as to how limited our understanding of the design is before it is actually realised, even with all the CAD involved in all stages of the process.
And that too will be a crucial test for 004/CV-20 - if the shipyards learn how to self-correct based on CV-18 and CV-19. This is very important for any large scale production. Yes, PLAN has demonstrated that it can achieve that on smaller vessels but it needs to do so on the really challenging designs - carriers and nuclear submarines.
Backward-compatibility requirements will result in the J-XDSH being constrained in terms of physical size and weight, which will introduce all the related limitations onto its operational capabilities (particularly internal volume, which directly impacts computing systems, power generation, combat range, payload capacity etc).
This is something that the USN must deal with, considering that the USN is to operate significant portions of their Nimitz CVNs until the 2050s, with every Nimitz having a 50-year service life (CVN-77 George H.W. Bush was commissioned in 2009).
The PLAN, meanwhile, are still at the beginning stages of their carrier fleet expansion efforts. Hence, the PLAN is afforded the luxury of going big from the get-go. Very fortunate, I'd say.
I don't think this is going to be that much of a problem. There is so much of a safety margin added to everything that is intended for combat use that it would take something genuinely non-standard, whether in size or maintenance requirements, to introduce problems. The carriers are designed to deal with aircraft that haven't flown, have flown, have crash-landed but retained usability and those that have crashed and are only good for spares. And all of that has to be taken care in the utter chaos of an ongoing military operation.
In short neither USN nor PLAN will run into too much of a problem, outside of core requirements like the catapult. More space, less space will just result in a few more or fewer aircraft. And it's not where the lines will be drawn.
Again, people who talk about carrier operations really lack the context of just how the carrier operations that they are familiar with differ from the carrier operations that the ships were designed for.
USN bombing Iraq or Syria is not the intended use for supercarriers. The carriers were designed for providing long-range offensive and defensive power against Soviet naval task forces in the projected battle for the North Atlantic. They were the very long-range anti ship missiles (two-stage: first stage reusable, second stage expendable) as well as very long-range anti-missile missiles (two-stage again).
From then the ranges have only increased.
Nobody in their right mind would ever decide to park a CSG next to a Soviet naval base so it is absurd to expect that this would be a present-day consideration. What the think-tankers and other talking heads say is largely irrelevant for the actual planning that the navy does.