Nintendo have said it themselves. The Switch is a hybrid. They have admitted it is a replacement for the Wii u but not for the 3ds. However, they are not gonna let the 2 cannibalise each others' sales indefinitely.
So far the Switch seems to have been marketed towards young adults/20+ and older. Seems like a departure from the family and child friendly Nintendo consoles from the past. The 1st party releases seem to back this up too. Blockbuster AAA home console on-the-go type titles. However, there is no way Nintendo is going to give up on a large part of its potential audience.
My prediction is simple. They will quietly drop the 3ds in late 2018 and then we will start to see more "handheld-like" game releases. Such as:- Mario and Luigi, Mario vs. Donkey Kong, Paper Mario and..... Animal Crossing. Also it will be around the time that Pokemon lands on a "home" console for the first time. These 2 handheld behemoths will be among the first, sometime in 2019 to go after the handheld crowd who will be searching for something to replace their 3ds's with. Of course, among that crowd will be children and family-orientated gamers. Slam dunk Nintendo! Get the hardcore on board first, then chase all the others once you have discontinued the 3ds. Now i know the 3ds is considerably cheaper but i believe part of Nintendo's strategy to catch all of the hanheld crowd too will coincide with either a price cut or a different/cheaper Switch Sku.
Just my opinion so please don't bash. (Too hard, anyway!)