Google has been deprecating, killing off support for, their old AJAX crawling scheme since 2015. It has been dying a slow death but now Google's John Mueller has said on Twitter is has been fully deprecated.
John said "We crawl, render, index the URLs with #! now, we usually don't use the ?_escaped_fragment_= anymore, so it's really deprecated."
It was scheduled to be completely gone by Q2 but lived on for a bit longer.
So I guess now it is completely not supported by Google? Anyone want to test it?
Forum discussion at Twitter.