After discussion here: whatwg/html#1929 there is rough consensus to modify the existing dialog focus steps to make the dialog element focusable by default unless there is a control within the dialog that has an autofocus attribute.
Since i do not have the chops to work out how the spec needs to change to reflect this, would like those who may do to help @travisleithead @adanilo @arronei @cynthia any ideas?

the relevant spec bits:
https://w3c.github.io/html/interactive-elements.html#the-dialog-element
https://w3c.github.io/html/editing.html#focusing-steps

Firefox are in the process of implementing (dialog available behind flag in latest nightly) and I am working with the FF acc implementers to ensure that the implementation has good acc out of the box.