Glimpse of Yaru MATE (work in progress) shared by Martin Wimpress. This is some news that should bring some joy/excitement for those waiting for an official theme revamp in future Ubuntu MATE releases.
There was some discussion about the new Ubuntu MATE theme in the works during an Ubuntu Podcast episode shortly after 20.04 LTS was released and I thought he was building something with Yaru-Colors but looks like he's been working with the Yaru team.
Note: if you already want to play with something Yaru-like for MATE, you can have fun with Yaru-colors (snap/source).