As a reminder, Nintendo said the DS wouldn't replace the Gameboy Advance.
This is a blanket damage control statement they can fall back on likely because they consider the Switch to be an experiment and they don't want to fully commit to it until it has proven itself to consumers and to themselves
They also had a real successor to the GBA (a Game Boy 64, if you will) in the pipeline in case the DS was a failure. I would not be surprised if we see an actual 3DS successor if the Switch ends up being a Wii U-level failure.