meta-freescale includes a class (machine-overrides-extender) to make it easy for a BSP maintainer to create, and a BSP user to switch between, multiple *sets* of configurations for a given MACHINE.

Why would a BSP want to do that? Because in some cases there are multiple choices for the user. For example: for the kernel, the user could choose either the vendor kernel or the upstream kernel. However, sometimes these decisions are "locked" together: i.e. if you want to use the vendor's binary blob for (say) graphics, then you have to use their vendor kernel as well. It's not possible for a user to choose, say, the graphics binary blob but want to use the upstream kernel too. Therefore the BSP ends up with "sets" of configurations which need to
be taken collectively instead of piecemeal.

I would like to see this functionality added to oe-core so all BSPs could take advantage of this feature without having to duplicate this class per BSP.

The class can be found here:
https://github.com/Freescale/meta-freescale/blob/master/classes/machine-overrides-extender.bbclass

An example of its use can be found here:
https://github.com/Freescale/meta-freescale/blob/master/conf/machine/include/imx-base.inc