I can even use manifest lists and have the same FROM for different archs: http://container-solutions.com/multi-arch-docker-images/ - that's what I meant saying that it's here. Just that it isn't advertised.

The problem is, Docker official images (e.g. alpine, ubuntu, debian, python, node, etc) don't do this, so every Dockerfile that uses those as a base needs to be edited by hand, and you have to trust someone for unofficial base images (or build and maintain them on your own).