Impractical - lacks usable defaults to produce a meaningful grid.

Nice try, but without the possibility to have fluid columns is pretty unuseful if you have to replicate a bootstrap 4 grid.
Add the possibility to set the number of columns and not the width in pixels.
The ideal would be to have number of columns and gutter width in pixel, so the width of the columns is fluid and they resize with the viewport.
Also add the possibility to set the first and last gutter to be half wide (or just see how bootstrap 4 works and add the gutter width to the left and right of every column)