Feature request: make callout markers keyboard-focusable

I really like the callout markers feature. The markup is easy to understand, and it was easy for me to override the colors in CSS. However, currently callout markers do not seem to be able to receive focus, so keyboard-only users aren't able to see them. Is this possible and I am missing something? If not, my request is for the callout markers to be able to receive focus and for the callout details to appear automatically when the marker receives focus and disappear when focus is removed — unless this proposal conflicts with other accessibility best practices. Thanks!