I'll say 5 million. It'll get a hardware boost from being early in the Switch cycle, buuuuuuut the fringe fans who are Ocarina of Time lovers IMO don't like cell shaded Zelda.
Of actual "Zelda" hardcore faithful the fanbase is smaller than people think it is. What Ocarina of Time/Twilight Princess managed to do was get more fringe fans because they were considered the standard epic adventure games of their time.
Cell-shaded Zelda simply sells less than Zelda games w/a grown Link + realistic graphics. Ocarina of Time and Twilight Princess wipe the floor with Wind Waker and Skyward Sword.
OoT and TP were able to break out and sell to more than just Zelda fans.







