A similar but older comment here.

columns.css is something I played with quite briefly. I left a note of it at WT:Vector 22 where this discussion was also raised. It's something that someone could take and make into a gadget potentially, but it's quite a bit of work to work around everything that is a table that shouldn't be, and it's hard to deal with a few other things besides as is immediately apparent there. For example, the fact that infoboxes and images are a part of .mw-parser-output makes it difficult for them to end up in the space we would classically prefer them in. Then there's the issue of tables that are very wide, which means you probably need to break the columns context.

One thing that I didn't like doing to work around that issue is target the elements within .mw-parser-output instead, since it breaks lists unintuitively relative to paragraphs. So that was a failed investigation point.

That said, this style really only works because Wikipedia is pretty good about sectioning their pages, so there's no guarantee it would look nice with a long long prose section (most often found on featured articles for the most part) or a narrow screens.