Recently I had (from an Infra side) to start deploying KVM guests for the ppc64 and ppc64le arches, so that AltArch SIGs contributors could start bootstrapping CentOS 7 rebuild for those arches. I'll probably write a tech review about Power8 and the fact you can just use libvirt/virt-install to quickly provision new VMs on PowerKVM , but I'll do that in a separate post.
Parallel to ppc64/ppc64le, armv7hl interested some Community members, and the discussion/activity about that arch is discussed on the dedicated mailing list. It's slowly coming and some users already reported having used that on some boards (but still unsigned and no updates packages -yet- )
Last (but not least) in this AltArch list is i686 : Johnny built all packages and are already publicly available on buildlogs.centos.org , each time in parallel to the x86_64 version. It seems that respinning the ISO for that arch and last tests would be the only things to do.
If you're interested in participating in AltArch (and have special interesting a specific arch/platform), feel free to discuss that on the centos-devel list !