Anyone else notice how soon after the last game this is getting announced? We've been accustomed to having to wait the better part of a decade for the next mainline console Zelda game. Ninty hasn't had the capacity to develop a modern AAA title in less than six years before. Now we're supposed to expect them to release a whole new game with the same size and scope as BotW - that took them six years to produce - in less than three? (Assuming a 2020 release date with no delays.)
To me that heavily implies they aren't trying anything new. Because from what I've seen the more gimmicks and foreign concepts a game has, the longer it'll take to make. I mean TP took...2-3 years? And one of those was just porting it to the Wii. So about 2 years. SS took 5. TP, whether you like the game or not, felt like it was overflowing with content between two collect-a-thons, upgrading to 5 heart pieces, and rupee chests stuffed up the wazoo in places they ran out of rewards for. Meanwhile it felt like they had to cut corners with SS, going back to 4 heart pieces, giving you three free hearts, turning two hearts into medals (that's 5 hearts * 4 heart pieces, meaning they basically subtracted 20 sidequests).
In my opinion, this clearly shows that the largest portion of time goes to figuring out foreign concepts, such as reworking the combat to feature motion controls or turning Zelda into an opinion world. If this is just more of BOTW, even if it is BOTW+, then it'd be much easier for them to create a new game.