With this Nintendo should be able to comfortably get the 3DS past the 70m mark within this fiscal year. Good announcement, because the only 2DS version that has been available before isn't exactly pretty and does not have a clamshell design.
Skimming a bit through this thread suggests that there are people who believe that this announcement could cut into Switch sales. That's not how it works though. This is going to add to the total of the 3DS family without taking anything away from Switch, so it can only be viewed as a positive thing.