Between Skyward Sword through Hyrule Warriors Definitive Edition - Nintendo has either released a new Zelda game or had one known to be soon released at all times. Through this time we've averaged 1-2 Zelda games a year actually.
Feels like 2019 could be the first time in awhile they let the franchise rest a bit. With as well as BOTW is still selling and Hyrule Warriors out there again, I don't think Nintendo is in a rush to bring on HD remakes or smaller Zelda games to Switch yet. Given none of those have been announced yet, the earliest those would seem to come is late 2019 - the time Nintendo presumably will focus on Animal Crossing, Pokemon and maybe Bayonetta 3 or Metroid Prime 4.
I predict NX launches in 2017 - not 2016