Getting the semantics right in complex tables can be tricky, especially for ARIA tables/grids. It would be helpful for authors to be able to use the Accessibility Dev Tools to check whether the correct row and column coordinates and headers are being exposed. Right now, they need to use a screen reader or similar to check this.

A real world use case for this is bug 1511275, where we're trying to fix the semantics in the Searchfox code view. Because of copy/paste and layout requirements, this needs to be an ARIA table instead of a simple HTML table. Andrew Sutherland (who is working on this) asked me what screen reader he should use for testing. While it's totally awesome that he asked, I was going to suggest that he use the Accessibility Dev Tools instead (which would be simpler for him), until I realised it doesn't expose table information.

I think this might also be useful in auditing down the line. For example, we could use it to flag data tables without headers, tables with only one row/column, etc.