Milestone 12 was completed on 2020-07-01. Besides adding support for the Q1 2020 releases of melodic, dashing, and eloquent, the release of OpenEmbedded dunfell and the release of webOS OSE v2.5.0, Milestone 12 makes significant changes to how packages that do not build are excluded from bitbake world and the *-image-*-world images, and alters the policy for selecting the versions of platform packages provided by OpenEmbedded (see Baseline Platform and Selection of Platform Package Versions). As of this milestone, the branches of meta-ros and meta-ros-webos will no longer be rebased; the [*-draft] branches will be kept coincident with their corresponding unsuffixed ones until they are dropped in Milestone 14.
A new revision 19 of the OpenEmbedded Build Instructions updated for this has been published. Its change log is here. A “rich diff” of the changes made since the previous revision is here.