Getting multiarch dpkg into Debian

Debian handles multiple versions just fine. In fact, during a transition (say gcc4.5 - gcc4.6), both packages are installed, along with their dependencies. Once the transition was done (no more dependencies on gcc4.5), that set of packages is automatically removed, unless you have marked them as manual install or pinned them. No weak technical foundation at all.

In this case, Debian is going beyond biarch to multi-arch. Not just have x86-32 and x86-64 (amd64) installed, but say have ARM, SPARC64, x86-32, and x86-64 simultaneously installed, to ease cross-development. That's hard, But Debian is working to get it right.