Why is it useful, who would benefit from it, how should it work?
A master release contains phases and milestones, along with the sub-releases which are part of it.
The phases and milestones of the master release are meant to be used to represent and help manage the combined delivery steps across all sub-releases.
Based on the above description, along with current priorities and community feedback, we are unlikely to make updates in this area. We hope you can understand.
We're having a Product Line that currently has 3 products following the exact same release cycle and plan, because our customers currently use the whole product line. But for each product in the product line there is a product manager and several product owners. So the idea is to plan the master release and then the POs can adapt this to their needs in the individual product