I'll reply here rather than in 054a thread.
What seems certain about 055: that it will bear the designation 055. While that seems very silly to point out, i wrote it here to accentuate the certainity of an incoming project. PLAN's history doesn't seem to care if the next surface combatant is a corvette, frigate or destroyer. They all get 05x designations, in historical order as the development projects get started.
Knowing that, and knowing that 056 is already building, it is quite likely 055 project has been started before anything even came of 056 project. Also, it came sometime after 054 project (but not necessarily after 054a project). Since all these projects are of different complexity, it is quite possible/likely they each need a different amount of time to complete R&D, design etc.
Maybe 054 was always planned to be 054a, from the start. But perhaps VLS and some other systems weren't ready. But hull and propulsion were. So we got a test batch some years in advance.
In the same sense, maybe 055 is in design and development since 2005. or whenever. And maybe, just maybe, the whole project is running late. Late in the sense that 052d is to 055 what 054 was to 054a, only in reverse. Meaning certain subsystems were ready, like VLS and radar suite, but propulsion/transmission werent ready. And without them one can't really make the hull either. While this is all just guessing, granted, there are cues and precedents for it. We know China has had problems with gas turbines, and even more so specifically with turboshafts. And marine turbines could be regarded as really big turboshafts.
What if 052d is really somewhat of an uplanned version? Maybe back in mid 2000s or whenever 055 was started, 052d didnt even exist as a plan. But its development got prolongued and PLAN leadership really wanted the new toys - radar/vls etc. So an interim solution was created.
Moving onto the next point. Does 055 has to be a large combatant? No real evidence is there for it, but i would agree here it is most likely. 054 is fairly recent, as is 056. So we have smaller end of future fleet covered. What is left is destroyers, which China does lack in numbers (One cant call Ludas destroyers really) and 052 hull/propulsion is of older design than 054 and dates to 052b, which would make it some 15 years old.
So, knowing that even the 052d does sport a pretty old fashioned hull, and knowing there's still relatively few destroyers, it's likely 055 is going to be a destroyer sized ship. If indeed development started sometime in the middle of last decade or perhaps latter years of last decade, it's also plausible we should see that ship within next few years.
I proposed before that 052d was perhaps a result of a 055 delay. There may be more explanations. Maybe 052d is a budget version of 055, if 055 was decided to be too expensive to be procured in large numbers. In my opinion that's still a bit less likely version as it'd still leave 052d with an old class hull, not really suited for a modern day destroyer. If true, it'd mean we could see yet another new class of destroyer soon, in addition to 055. IF 055 is a 12000 ton behemoth (which we don't know, no proof yet) then a whole new class of technologically similar but size-wise a bit smaller destroyer is plausible. But frankly, so many different classes and subclasses launched within a decade or so all performing similar roles doesn't seem too likely.
As a final side note, is it not possible CCTV made a mistake when they said 6400 was full displacement of 052c? cctv isn't always accurate, plus the matter of displacement is really often mixed up even in serious military publications. Comparing with other ships in history and their sizes, 052c really does look as if 6400 would be its basic displacement. Unless the ship has a record shallow draft. Which, when takes into accoun the heavy systems and superstructure it sports - doesn't seem likely.
