I suspect this mod is playing out more or less precisely like the 052B one. A guess.
Standardizing the sensor and AAW suites of the non-"aegis type" destroyers (i.e.: 055, 052D, 052C), and the destroyers produced post the original 052 pair, with what is essentially a 054A level kit, makes a bit of sense.
The four Sovremennys, two 052Bs, two 051Cs, one 051B, basically end up as uber 054As with moderately enhanced anti surface capabilities, greater range/endurance, and so on.
Depending on the size of the surface combatant fleet the PLAN ultimately want, and depending on how the pace that they produce new destroyers at (not just 055 and 052D, but also the expected next generation of large and medium destroyers), I wouldn't be surprised if the MLUs for these ships is also part of a desire to enable them to be in a more "mothball-able"/reserve-fleet condition than their pre-MLU state.