Really good to see the Internet Explorer team working on this. Responsive images are a nuisance to implement until they are widely supported across the major browsers.
The official status of
srcset is on the Modern IE Status website. The
picture element is still under consideration, but even
srcset is a step forward.
Also under development: the
main element (status) and date-related input types (status).
There are still many steps to be taken, but I see
srcset as key ones to match the other browsers and to accommodate modern web development. Love it or hate it, Internet Explorer is still a significant browser and these signs of progress are encouraging.