I'd say that should the 122mm and 300mm MLRS of the PLAGF be containerized for ship-based launches, then it'd certainly be a considerable plus for fire volume and coverage against enemy-held land positions.
The obvious downsides would be shorter strike ranges compared to PLARF missiles (which would necessitate getting closer to the enemy shorelines/beachheads) and requiring the carrier ship to be pointed at the direction of the intended targets to be effective. Despite this, provided that the MLRS uses guided rockets, then it shouldn't be a major problem for the latter.
For Taiwan's case, apart from granting an greater volume of offshore-based firing solutions for the heavily-populated western side of the island (in addition to shore-based firing solutions against targets on Taiwan that is withing PHL-16's strike ranges from the mainland), it also opens up the less sparsely-populated eastern side of the island where it would be challenging for the 300mm and 370mm MLRS from the PHL-16 to cover effectively from the mainland side.
In such scenarios, strategic ROC military sides located on that side of the island, such as the Hualien and Taitung air bases would become open for sustained bombardments to hinder any meaningful repair efforts after initial strikes by the PLARF, PLAAF and PLAN.
Beyond Taiwan, there's also the Ryukyu Islands. The entire island chain is located beyond the reach of even the 340mm PHL-16 MLRS, with the closest inhabited island (Yonaguni) being at least 380 kilometers away from the mainland. Across the entire PLAGF's land-based arsenal, only the 750mm TBMs from the same PHL-16 can reach those islands from the mainland. Hence, should there is a need for Operation AR to include the liberation of the Ryukyu Islands, then such systems certainly are way more useful than otherwise.
Essentially speaking, this idea sounds roughly similar to the LCT(R) from the WW2.
But of course, this isn't exactly a novel idea - The 716th Institute is working on/has worked on one such example (albiet with a much larger diameter and strike ranges):
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