Circling back and noticing your background, I’ll also mention there’s a pretty good post by David Shanske Converting WordPress Themes for Microformats 2 that goes through some of the changes one would want to add to a theme to make them more IndieWeb friendly. At the bottom of that post there’s also a comment by me about a GitHub repo that has a step-by-step set of changes that adds microformats v2 to the TwentySixteen theme. (Be careful though as some of the changes also gut Post Formats out of the theme in lieu of support for Shanske’s Post Kinds Plugin.)
My coding skills aren’t what I wish they were, but I was going to file an enhancement for Anders Norén’s new TwentyTwenty theme to support microformats 2 following his thread with Kevin Marks and Tantek Çelik at WordCamp US. Having proper, modern microformats in annual themes could help to provide better examples for other developers and themers.
Ideally, it would be awesome to see WP core upgrade to microformats2, and because it’s not recommended that these classes be used in combination with CSS (they’re solely for semantic purposes) it shouldn’t cause any backcompat issues that I can think of off hand. (There also shouldn’t be any issues for the older microformats1 to sit alongside microformats2, which means that they can co-exist–the parsers that use them will correctly chose the correct ones.) Sadly, it’s beyond my pay grade to attempt such a change or to wrangle the necessary buy-in to attempt it. If it’s an area you’re interested in pursuing or learning more about, I’m happy to chat about it at length.