The 052D is their top of the line destroyer... at the moment. And at all accounts they will be building 12 of them (things may change in future, they might order another 6, but it is unlikely at this point).
The number of potential 055s is directly linked to the kind of navy the PLAN wants to field by 2030.
I personally expect an equal number of "frigates" (054A, and its successor), and "destroyers" (052C/D, 055). So if we use 72 FFG + DDGs combined, we'll have 32 of each
(I lump 055 as a destroyer, and 054A's successor as a frigate, because both I expect will be larger than what is traditionally called a destroyer or frigate respectively.)
The question therefore, is whether the PLAN will seek to develop a 7000-8000 ton sized 052D successor, or if they will simply cease production of 052D sized vessels in favour of the heavier 055. In that sense, buidling 30 055s by 2030 might make sense, because by then, all the DDGs built in the 2000s and earlier will likely start to retire. So that are the pairs of 052C, 052B, 051C, and everything before it (the four sovremenny's, the 052s, 051B). So that is 13 vessels that will need replacing by 2030, if not earlier (considering those ships will have quite done quite a few voyages by then).
Will the PLAN replace them with a new 8000 ton DDG? Or just the 055? If it is the latter, then 30+ 055s may make sense, especially if we consider that the PLAN may seek a larger navy overall. 30 055s combined with the preceding 16-18 052C/Ds, will make about 48 "DDGs".
In my mind, I can imagine the PLAN seeking a fleet of ~100 modern, "A team" surface combatants, similar in number to the current USN's combined burke + tico combo. The difference is that half of the 100 surface combatants will be FFGs made up of 054A and its successors, so the PLAN will be less top heavy, and will still displace much less than the USN's surface combatnat force of combined DDG, CG, FFG, LCS displacement today.
Given the PLAN's expected economy and global interests by 2030, such a fleet composition is not unreasonable imo.
(I suppose I'm seguing into future fleet composition now, but whatever)
So my idea of the PLAN's "critical mass" surface combatant force by 2030+:
48 "DDGs": 052C/D, 055/A
48 "FFGs": 054A, 054A successor
This will be an effective doubling of fleet number for their current blue water capable surface combatants, and a manyfold increase in blue water capable combatant tonnage and capability. It may seem a lot, but considering by then, the PLAN will likely start to retire their shorter ranged 022s, 056s, and other shorter ranged ships, it is more reasonable. They will have plentiful personnel and facilities to reassign.
That said, I expect the PLAN will retain a force of 056 displacement light frigates for lower intensity missions in the region, but that depends on the geopolitical climate.
. I think my point was mostly just that the number may look suspicious, but it's not so unreasonable that we can rule it out. It would certainly be a very dramatic change, but over the span of 20 years if this is the force they want to build it's more doable. Even if it's not 30 055s but 30 054s they would need to expand the number of yards that could handle that capacity, and, to be frank, I don't think 30 more DDGs is an unreasonable number for the PLAN. When we're talking about a span of time this long geopolitical forces have a large role in determining the final force count but if I were to throw my hat in on a number right now, 50 might not be a bad ball park figure for DDGs (but then I think the PLAN is aiming to greatly expand its reach, even outside of the Pacific).
