Honestly, I don't think that it would be too hard. With the grid function you can do a lot of things, specially because you can use grid.cell(rowspan:3, colswap:4) to make cells that span multiple rows or columns, use fractional sizes for the columns (1fr, 2fr, etc), and add independent insets and strokes for each cell, so you can already do a lot of the things you can achieve with css flexbox.

Though I suppose the docs could include tutorials for how to use them to make a more diverse kind of documents, and adding another layout function that behaves more like flexbox would be nice (though it wouldn't be too hard to create a function that re-creates the behaviour of flexbox based on the grid function).