The original zelda game was planned to be able to travel between a mideval setting and a scifi setting.
Also who says a futuristic zelda will represent anything close to our modern world or what we consider "futuristic".
It's likely if they go that direction it will be a very unique and new interpretation of a scifi world. One that mixes scifi and fantasy together. So if they do go in that direction, I perfer a wait and see attitude.