The use case I needed this for is a build pipeline where the initial build sets the project version to major.minor.buildnumber. This way the resulting artifact can be tested and when tests are passed, this same artifact can go into production. The idea is that every commit is a RC.
These new variables makes it much easier to do as I can pass these new variables to the maven plugin versions "set" goal and use it directly in the build name setter plugin. In my current build I'm using a combination of maven-help-plugin and some scripting, build helper maven plugin and the versions maven plugin.
The NEXT_x vars can be used if you want to automate release branches. First you create a release branch and then you update the development version in the develop branch. This is not really something I need, I just added the same variables as the build helper maven plugin uses in its "parse-version" goal.