Zelda is a bi-annual - sometimes annual if you count re-releases.
It's a bankable franchise that drives hardware - so you gotta believe Nintendo wants another one ASAP once BotW sales slow down.
If they simply reuse BotW's engine and accomplish something similar to Majora's Mask - I'm sure fans will immensely enjoy that. Not every Zelda game has to be a technical breakthrough (few Zelda games truly are tbh).
Don't underestimate Hyrule Warriors 2 or possibility of other Zelda spinoffs. What game studio wouldn't want to work with Zelda?
I predict NX launches in 2017 - not 2016







