Plan for YAML Content 8.x-1.x-alpha6

This issue will serve as the parent ticket to identify new features merged and lined up for release in the 8.x-1.x-alpha6 release. All child issues of this ticket will be included in that new release, and newly completed issues should be associated here to continue that tracking.

Primary focuses for this release will include:

#2944221: Drush create-new option has no effect