I am aware that similar propositions have been made, but no solution has been found for this scenario, which is very common in our organization.

Suppose there are stages that are project-specific, i.e., S1, S2, ..., Sn, and stages that are project-independent (can be factored out into shared lib), i.e., I1, I2, ..., Im. A pipeline for a project should contains both the project-specific stages as well as the project-independent stages, the latter possiby multiple times, e.g.,

S1, S2, ..., Sn, I1, I2, ..., Im, I1', I2', ..., Im'

It would be great to be able to define such a pipeline like this:

pipeline {
  stages {
    stage ("S1") { ... }
    stage ("S2") { ... }
    ...
    stage ("Sn") { ... }
    sharedStages()
    sharedStages()
  }
}

def sharedStages() {
  stage ("I1") { ... }
  stage ("I2") { ... }
  ...
  stage ("In") { ... }
}