In my opinion replacing the H/AJK-16 with the U-VLS on the 054B makes sense if there is (or will soon be) a new missile that can be quad packed "ESSM style" in the U-VLS and is good enough to replace the HQ-16 for medium range air defence. In that case even a 16 cell U-VLS would be better than the 32 cell H/AJK-16.
Yes indeed they are planning on a new medium ranged SAM one that is going to be bigger than lets say a navalized PL-12. A good example would be something based on the 9M96E2 missile which I will use as a guidepost for a missile that is quad packable and still ranges up to 120km. Now an H/AJK-16 is no slouch in terms of size, an HQ-16 is not a small missile either, and there is likely room for quad packing missiles the size of a PL-12. Question is the length of the missile. The 9M96E2 is about 5.65m in length, and the H/AJK-16 has to be over 5 meters in length, as the HQ-16 is about 5 meters. The Shtil-1 is about 5.44 meters. That probably doesn't give much of a margin unless the H/AJK-16 is around 5.8 to 6 meters in length (5.8m if the H/AJK-16 is copying the shorter Mk. 41 Self Defense version). The actual 9M96E2 is cold launched though, which means additional length must be considered for the compressed gas canister. So its more likely the U-VLS with the 7 meter length would be a more comfortable fit with margins to spare.
However, until a Chinese equivalent to the 9M96E2 missile is introduced, the U-VLS is oversized for single HQ-16s, and while I have heard about the U-VLS claiming to be able to support HQ-16 (and other missiles like DK-10 and YJ-83 and so on) I have never seen test tired on one unless maybe the Type 055 or a special test ship that can demonstrate that using a digital beam forming X-band radar that can work for target illumination. The Type 052D can't test this since it lacks X-band target illumination, with its being on C-band. HQ-16 would certainly require its own concentric canister to work on a U-VLS, though that should not be a problem to develop one if one doesn't exist for it currently. As a final note, the 9M96E2 has active guidance and would spare the ship from having ship board illumination, and if the PLAN develops a similar equivalent using PL-12/PL-15 seeker, that would make things a lot simpler.
If the new frigate decides to use HQ-9, you will likely need to create a frigate version of the Type 346, maybe a single or dual panel, maybe each panel smaller, that spins around with a radome to cover it. That won't be unlike the "pineapple" radome we have been seeing in drawings and with an actual test mockup on Wuhan. Small fixed panel C-band illumination arrays would have to be set on the mast supporting the "mini-346" for HQ-9 target guidance. Not impossible to do, and the ship will keep the X-band Type 366 and 344 for ASM and gun fire control.