too early to say...
If Nintendo focus all power on switch, and it becomes a unification of Hanheld/homeconsole whit titles like pokemon (main series), Fire Emble and others... i think Nintendo will be fine and will hit at the very least 35 M consoles util PS5 or late 2020- early 2021. if we get a good price drop, to something like $199, and a new model whit a much better battery 40M, or more, becomes a real possibility.
but...
If Nintendo makes a dedicated handheld (3DS sucessor), and starts to treat Switch as the "portable home consoles"... well.. Switch will have a painfull death like WiiU, i predict less than 20M, perhaps even less than 15M...
edit: also, there is a huge chance that nintendo will lauch a sucessor for switch at the time Ps5 comes to life... Switch sucessor at 2020-2021 it's something that is alson on the table.







