For data tables, it's important for accessibility to be able to identify table row and column headings. Since most tables inserted in a post should be inserted to display data, it should be the default assumption that there's at least one row and one column heading. Right now, the default code does not add any headings or scope and I can't see a method to specify headings. E.g. <th scope="row"> or <th scope="col">.

It's also not possible (as far as I can see) to create <thead> or <tfoot> elements.