Maybe it's just me, but I think having a possibility on Pipeline and Multibranch Pipeline projects to block execution while up- or downstream-projects are building would be beneficial, especially when migrating existing installations (see my posts in stackoverflow and in Jenkins CI).
With Freestyle and Matrix projects there was the option of going to the "Advanced Project Options" and specify that the build should be blocked when upstream/downstream project is building. For Pipeline and Multibranch this option is unavailable, and I did not find a means of synchronizing a Pipeline/Multibranch project to existing freestyle/matrix projects without orchestrating this in another pipeline script. However, having to do that with an installation of about 400 inter-dependent projects is a huge block of work that has to be sorted out in one go. Having those "block when upstream/downstream project is building" options would allow for a gradual and smoother migration.