Stopgaps? Between what and what?
Between Nintendo's significant consoles. The Gamecube and the Wii U have their cult-like fanbases who think these consoles are like the Messiah, but they weren't major Nintendo consoles; it doesn't seem Nintendo ever saw them as such, either. While N64, Wii, and Switch marketing were all prominent, all over the place, the Gamecube and Wii U were rather mute; in addition, Nintendo didn't release any major flagship titles/killer apps for Gamecube or Wii U.
Most importantly, Gamecube and Wii U never had a major interface upgrade - they were more or less, "hmmm, we need to have some kind of upgraded hardware to fit the timeslot, but we don't yet have our next big thing concept ready" - which is really the main reason why they are more like stopgaps.
I describe myself as a little dose of toxic masculinity.