In T180867#3772078, @RexxS wrote:

The choice of cells for markup for row headers and row scope is rather more problematical. Priority should be on adding scope for column headers as that should be easily achievable and much less likely to encounter opposition.

The other really significant addition would be for VisualEditor to encourage editors to add a caption by setting the default property to 'on', but whether that should be considered in this thread or separately is debatable.

(The caption idea is now T181173: Improve accessibility by encouraging editors to add captions to tables.)

I'm just discovering that scope are not added with the Visual Editor, nor that it's easily possible to add them without switching to the classic editor. On frwiki, the community relies on a gadget to detect this type of inaccessible table. The impact is quite significant: we continue to generate inaccessible tables that have to be corrected by hand.

In T169306#9730199, @Lofhi wrote:

I'm just discovering that scope are not added with the Visual Editor, nor that it's easily possible to add them without switching to the classic editor. On frwiki, the community relies on a gadget to detect this type of inaccessible table. The impact is quite significant: we continue to generate inaccessible tables that have to be corrected by hand.

WRT impact; scope is not as important as some people make it out to be. Screenreaders etc will simply guess and are actually pretty good at that. Only pretty complex / inconsistent header application (when there are td gaps between headers for instance) really requires the scope attribute.