I really don't like how disingenuous, propagandistic and patronising Simmons is being in this article. Ending each section saying "all this will be impossible if not done the way I like", which is absolutely not true. There's not one reason why anything that can be done in "display: grid" couldn't be done with "display: masonry".
But I think, and I hope, that people aren't the fools she's taking us for, and can see how absurd her proposition is.
You could basically clone the grid specification, if you want all those features, and that way both can be developed with what works for each. She says doing that means new grid features might take more time to come to masonry. Really? More time than having to deal with new grid features that won't work at all with your version of masonry integrated in grid? You're still having to deal with two layout systems, even if you want to disguise one of them. Except doing it your way you can't select which system gets the features that work with it.
At the end, instead of two layout systems with two complete sets of features, we'll have one single layout system with a bunch of features that sometimes work and sometimes doesn't, depending on a particular value of a particular declaration that you'll have to know about. And that's why people hate CSS.
Seems lazy and an absolute mess to maintain. And it doesn't make sense at an intuitive level, since masonry works similarly to flexbox, not grid; and it doesn't make sense at a logical level either, since a masonry layout is not a grid.
But I guess this is what we'll end up getting, since apparently anything Jen says goes. Like the ridiculous idea of doing "CSS4", which means nothing, does nothing and is nothing, but we're going with it for some reason anyway.