If 052Ds and 055s go into large serial production, is there even a need for a next gen frigate? A next gen frigate is supposedly higher in displacement which means it would be closer to 052D size anyways.
Personally, I think that there should always be a blue water capable frigate class in the Chinese Navy -- a ship which is slightly smaller and less well armed than a current generation destroyer of its equivalent generation. Such a frigate should be built in significant numbers to take up lower intensity missions independently and to conduct escort duties for convoys, slower replenishment ships, and to contribute to the AAW and ASW picket especially for large task groups.
ASW especially is a mission where risking a frigate is far more sensible than risking a large destroyer like 055 or even a destroyer like 052D, given the smaller size, less weapons, less crew and of course lower cost of a frigate makes it more sensible to risk versus an undersea opponent which can be anything from a billion dollar SSN to a cheap small mini SSK. A frigate would likely be less well armed but equally well equipped with ASW sensors vis a vis destroyers, thus its crew also have more time to specialize and train in ASW missions compared to destroyers, which may be equally well equipped with ASW sensors but a destroyer also has a variety of other more capable weapons and sensors such as anti air warfare and anti surface warfare where attention and training must also be placed, potentially giving them less time to train in the ASW role compared to a frigate.
Overall, I expect the Chinese Navy to still pursue a new generation frigate successor to the 054A class and that such a class would be built in large numbers alongside relatively large numbers of 052Ds and 055s.
Of course the linchpin of my belief rests on certain assumptions of the future size of the Chinese Navy. I believe the new generation frigate will be built in numbers equal to 052Ds or 055s, at least. Therefore, if a large number of 052Ds are built (12 expected but rumoured up to 24) and if a large number of 055s are also built (4-8 expected, but a few rumours have put it up to a whopping 24 -- take it well salted), then I expect a similar number of new generation frigates (anywhere from 12 to 24) to be built.
Needless to say, 24 frigates could be built and possibly even inducted and commissioned by the Navy effectively within a decades time when one looks like 054A's construction rate (if construction of the new frigate begins within a year or two), and by that time the current 24 054As will still be in service as they will still be very young.
Therefore, how big will the Navy's surface combatant force be, in the late 2020s? 24 054As, 12 052Ds, 4-8 055s, and 12 or so new generation frigates? Or something much more dramatic, such as 24 054As, 24 052Ds, 24 055s, 24 new generation frigates?
It's impossible to say, but I do think the Navy will likely build a new frigate class that matches or exceeds the number of 052Ds in service to complement the older 054As.