Milestone 11 will introduce support for OpenEmbedded release series newer than thud and migrate webOS OSE to version 2.x. This means that meta-ros will be able to be built for Raspberry Pi 4. In order to reduce the number of combinations of OpenEmbedded release series and MACHINE-s for which we do builds, we intend to replace building for raspberrypi3 with building for raspberrypi4. However, we won’t do anything that knowing prevents others from building for Raspberry Pi 3.
If this change will cause you hardship, please respond on this meta-ros GitHub issue by the end of 2020-01-17.