So... Nintendo made the same mistake twice? For context, the Wii used GameSpy under-the-hood. You weren't necessarily required to use it (as evidenced by EA shipping their own system) but most developers did. The reason why Wii online was shut down was specifically because GameSpy got bought out and started massively increasing their server hosting costs. Of course, that's a little different from the Rendez-Vous situ…
That being said, Nintendo has started using an in-house replacement system called "NPLN" in some of their more recent titles. Some examples include Splatoon 3 and Pokémon Scarlet/Violet. (They've shown no indication of converting older titles to the new system, however.)