I frequently use css columns property to style many parts of my site, but I have to add this as a custom class to a container block and use custom css to style it. This works really well on the front end, but obviously, does not display in editor.
Why this should be part of a core block:
It is unlikely that it will be created as a third-party stand-alone block as it has to be used as a wrapper. The container block is an ideal block for this.
Css multi-columns property produces fluid and responsive text layouts with just a few parameters (even beginners can get it!)
Css columns layouts cannot be achieved with existing blocks (e.g the columns block) as they do not flow text between them, hence, it has a distinct use-case compared to other column/grid options available in WP right now. (It might be called “text columns” to avoid confusion with the standard WP columns block.)
I think css columns is ideal for a core GB block as it adds versatile core functionality, without bloat, and is not just a pretty gimmick (which, I’m sorry to say, some Gutenberg blocks tend towards)