I didn't actually test it but it does look like packagegroup-self-hosted-extended needs to be modified after current python3 changes: it currently lists only these python related dependencies: python \ python-compiler \ python-git \ python-misc \ python-modules \ python-rpm \
Got a patch, just testing.
The meta-overc layer, [which for the purposes of this bug can be considered build-appliance plus a kernel and grub so that it can be booted directly] had the same 42 or so python3 packages that build-appliance has. In order to get meta-overc to be able to build all the various meta-overc image types (half a dozen or so ; some complete with full X11/gnome) including itself, I had to build and install the following extra py3 chunks. rpm -ivh python3-multiprocessing-3.5.1-r1.0.core2_64.rpm python3-mmap-3.5.1-r1.0.core2_64.rpm rpm -ivh python3-sqlite3-3.5.1-r1.0.core2_64.rpm rpm -ivh python3-debugger-3.5.1-r1.0.core2_64.rpm rpm -ivh python3-json-3.5.1-r1.0.core2_64.rpm rpm -ivh python3-xmlrpc-3.5.1-r1.0.core2_64.rpm python3-netserver-3.5.1-r1.0.core2_64.rpm rpm -ivh python3-pydoc-3.5.1-r1.0.core2_64.rpm rpm -ivh python3-curses-3.5.1-r1.0.core2_64.rpm rpm -ivh python3-resource-3.5.1-r1.0.core2_64.rpm rpm -ivh python3-unixadmin-3.5.1-r1.0.core2_64.rpm The double pkg lines are to solve dependencies. A full world build might uncover one or two more, but this is a good start.
To be honest for a build applicance I'd ship python3-modules and get the full Py3 standard library.
oe-core ee627d7a833e0d85f691729c4d2f774516a8f425 moved from Py2 to Py3, and 055e58e5cc73263a4112d5935ec871c3adf4cd9b added back Py2 for coverage as some modules we build still use py2.