Sorry @Permakai no updates on that. I’d love to see it happen too! Just waiting for someone to step up and either sponsor it or code it themselves!
Related, for anyone who wonders how this stuff gets done generally: How things get built... (from ideas to code)
I’ve been very tempted to get started on this myself a few times (I really want it too!), but always pulled away by more immediate responsibilities. For what it’s worth, one of the first things I want to figure out is this: [META] Plan entity relationships with metadata [#3187877] | Drupal.org