They did the same thing with the GBA and the DS. They're saying it to placate all 12 Wii U owners, but of course it's going to replace it.
The real question is whether it's also going to replace the 3DS. The 3DS has actual popularity and games, not to mention some features that would be sorely missed on a Switch (dual screen). On the other hand, having a single platform for both handheld and console games is very appealing to publishers, so Nintendo might try to push for that.
Or maybe eventually they'll release a smaller, cheaper Switch that's meant to be purely handheld, who knows.
