As my comment is one of the ones you call out, I'll write a few words. I'm perfectly clear on the significance of Zealandia, and I find it potentially very interesting.
That said, there is plenty of continental crust that is under water. Zealandia is a particularly large and reasonably isolated piece of submerged continental crust. To me, however, that does not make it a continent; it makes it a particularly large and reasonably isolated piece of submerged continental crust. Semantics? Yes, absolutely, that is semantics, and not terribly important, but sometimes, I get irked by semantics. :)
The same thing goes for Pluto, too, lots of astronomers don't really agree with the new "official" definitions, and it's unclear if these new definitions will hold up as additional planets/dwarf planets are discovered and observed more carefully.
That said, there is plenty of continental crust that is under water. Zealandia is a particularly large and reasonably isolated piece of submerged continental crust. To me, however, that does not make it a continent; it makes it a particularly large and reasonably isolated piece of submerged continental crust. Semantics? Yes, absolutely, that is semantics, and not terribly important, but sometimes, I get irked by semantics. :)