Export customers generally want equipment that has a proven record of performance and reliability, an established logistics chain, and domestic service buy-in as a guarantee of long-term support.
I don't think there is any real issue using the older VLS. 054A doesn't have the radar for and is clearly not intended as a long-range "shield type" AAW platform, so it doesn't need to fire HQ-9 or successor missiles. Anti-ship or land-attack missiles can be mounted in box launchers. The only real issue is a probable lack of compatibility with the future 5-5-5 quad-pack missile. But even on that score, HQ-16 is likely to outperform it on a per-missile basis. Even if 054B and all future PLAN warships are equipped with the universal VLS system, PLAN will still be using the older system for at least the next 25 years, and HQ-16 itself has considerable future development potential, being almost as large as SM-2.
Both SM-2 and the Buk missile are almost exactly 700kg, the SM-2 around 707kg and the Buk around 690 to 715kg. Given the HQ-16 is a copy of the latter, its safe to assume the same weight range. The SM-2 is around .34m in diameter while the Buk or HQ-16 is around .4m in diameter.
It stands that the H/AJK-16 VLS might have similar cell dimensions with the Mk. 41 except on length. To hold quadpack smaller SAMs, all you need is enough X and Y dimensions of the cell, and not the Z (depth) of the cell. For the H/AJK-16, it has to be over 5.5 meters in depth in order to accomodate the HQ-16. It would be comparable with the air defense versions of the Mk. 41 which are limited up to 5.3 meters in depth, but not the Strike and Tactical versions at 6.8 meters (Tactical) and 7.7 meters for the Strike, which are meant for Tomahawks and the SM-3. It stands possible that the H/AJK-16 as it is, may hold quad pack SAMs, with cruise missiles being out of the table.
Given that the DK-10 appears to be rejected by the PLAN in favor for the mystery 5-5-5 missile, DK-10 could be approved for export. Its land based version, Skydragon 50 or SD-50, already has been exported like say, Morocco. I don't have the length of the SD-50 but it should fall well within the length of the HQ-16. Potentially, four DK-10/SD-50 can be quadpacked into the H/AJK-16 cell. DK-10 will not perform as well as 5-5-5, with its maximum G stated at 38G, while 5-5-5 is up to 50G, the DK-10's speed may only be Mach 3-4, while the 5-5-5 reaches Mach 5. That is what you get with a smaller and older missile design. Nonetheless, the DK-10 performs similarly to the SD-10 used by FC-17 because the DK-10/SD-50 is a sea/land based version of the SD-10 which is the export PL-12. As such, it will also carry an active guided seeker.
There is no certainty or proof that the PN has ordered the DK-10/SD-50 but I believe that should be a viable ESSM like option for the 054A/P's VLS.