There is a proposal to clarify how to use parallel with declarative, using stages. This has the benefit of allowing config items that naturally live at stage level to be in parallel branches.
A sample here: https://gist.github.com/abayer/bbe18e779696af88af9208f7502b898c
The declarative ticket for this feature: https://issues.jenkins-ci.org/browse/JENKINS-41334
- Plan what adaptations are required for the new model
- Plan what impl/design is required for editing stage options at the parallel branch level