Hello,
Multiarch gives the ability to store libraries in the main root lib directories from different architectures and this allows applications to co-exist on the same system. Some applications are compiled for amd64 while others are for i386 and perhaps x32. This could have been done using chroots and for a long time prior to Multiarch it was. The problems of, what happens when a i386 app loads a library for amd64 were handled.
Now we've a similar situation for releases and even distributions. We can run multiple releases using a chroot for each, but perhaps this system can be improved on. Along comes the idea of supporting Multirelease. Certainly there is a lot to work out and I'm sure there will be plenty of ideas and good solutions.
Cheers.