Mine goes in for its second service next week and I know, following some slight "pressure" from me (and the fact I am a long-time client of the particular dealership), that the workshop manager has been "researching" this with MG to ensure that "everything is up to date" on the car.
The "pressure" was me referring the manager to the posts earlier in this thread (where members report what they had been told, either directly by MG or by their dealership) and "asking" that he "contact MG"
My understanding of this specific issue of Tesla Superchargers is that MGUK consider the upgrade to be "optional", so not "required" and thus not something for a "recall". As others have pointed out, this seems remarkably short-sighted!