I think the closest things done related to planes is References are not preserved after imports · Issue #1010 · Slicer/Slicer · GitHub which was prior to markups refactor, but includes work for a vtkMRMLMarkupsPlanesNode.cxx.
Related topics
| Topic | Replies | Views | Activity | |
|---|---|---|---|---|
| A user's proposal for Markups Module enhancements | 20 | 1685 | August 16, 2018 | |
| New Annotation for Slicer - Splines and Planes | 6 | 1003 | September 9, 2018 | |
| Markups for angle, line and closed/open spline | 5 | 994 | January 11, 2019 | |
| How to replace the annotation fiducial placement widget with the plane fiducial widget in AIAA | 0 | 239 | September 14, 2020 | |
| Craniosynostosis surgery planning | 3 | 905 | October 3, 2019 |