DKIM2 is (probably) on the way, and sooner than you think
The DKIM Working Group are developing a spiritual successor to DKIM. They have named it DKIM2 but it is more of its own thing than an iterative new version of the original DKIM protocol. As of now (June 2026) it is still going through the drafting process so there is no RFC or stable specification to develop against. Ideas are still being stress tested and edge cases considered. The latest Internet-Draft can be viewed here and there is also an explanatory website operated by the WG here. ...