I (@isabel_brison) facilitated the meeting based on this agenda.
Full meeting transcript on Slack
First point: how to set standards for using CSS grid in core, especially regarding browser support
I launched the question: why use grid?
And proposed its main advantage for us is in complex multi-column layouts, in particular if they have dynamically sized columns (such as the columns block).
@laras126 mentioned grid may be more performant in rendering versus flexbox, based on this blog post.
@peterwilsoncc suggested using grid with @supports-based fallbacks, whether using the non-standard IE implementation of grid or otherwise.
I suggested a progressive enhancement