I do think another big Zelda game is being made from the ground up for next gen. I think this primarily because they are making another Zelda game for the end of this gen with the same engine.
Let's look at the past when this happened:
OoT launched Nov 1998
Mm launched April 2000, a year and a half later.
WW then launched December 2002, two and a half years later.
I think it's pretty evident Nintendo usually takes 4-6 years to make a 3d Zelda game when they aren't using a prior engine. TP came out in 2006 so they spent about four years on that one. Skyward Sword in 2011. Botw in 2017.
Based on this pattern, I think Nintendo is low key making another full fledged Zelda game that will probably release 2021 or 2022 whenever Switch 2.0 comes as a launch exclusive.