While he termed his post as "my own speculation", I do believe that he/she have access to enough information/indication on the development of next-generation PLAN surface combatants, particularly on the first two.
New FFG will have a larger displacement than 054B but smaller than 052D, max speed and combat speed will be faster than the 054A but 32+ knot speed drifting is out of the question as it was not required in the tender.
Given the news from just earlier today indicating CODLAG propulsion system to be used on the PLAN's next-generation FFGs, the FFGs will certainly be larger than the 054/A/B FFG family, and should also form a new FFG class of its own.
The next-generation FFG should be somewhere around the 6000-ton displacement mark at full load. I wouldn't expect too much of a significant weaponry volume upgrade, though - Albeit the radars, sensors and computing systems certainly will have a leap over the 054/A/B family.
New DDG should have greater range and firepower than 052D hence will be bigger. It's expected to be similar in size/classification to the Burke III but incorporate more advanced sensors/weapons.
Given that the next-generation FFGs will have CODLAG propulsion system, it is only natural to expect that this next-generation general-purpose DDG will either utilize similar propulsion system configuration, or IEPS. Significant upgrades in both the weaponry and radars + sensors + computing systems are to be expected. And again, given the contrast between possible CODLAG/IEPS on the next-generation DDGs and the preceding 052D/DG DDGs, the former should be forming its own new class of DDGs.
In the meantime, SOYO mentioned that the present-day 052D/DGs in the PLAN is pretty much similar in terms of size and (mission) configuration as the Flight 1/2 Burkes in the USN, so it'd be interesting to see what this 9000+-ton full-load displacement 052D/DG-successor DDGs will be like.
And same for both the next-generation FFGs and DDGs - Endurance and integration of unmanned systems should be key considerations in their designs.
For 055 mod. and CG, these are basically top tier product hence it is very difficult to find info on them. If they do indeed exist, the construction period will be long so stay patient.
Expected, given how the first 055 DDG was commissioned just 5.5 years ago. Besides, there are still plenty of variables to set.