upgrade from x86 to amd64

[Morty <morty+debian-amd64@frakir.org>]

What would it take to automate an upgrade of Debian x86 to amd64?

I know there is no currently-supported way to do this.  What would it
take to make one?

Advantages: shops with a mix of x86 and amd64 systems can have one
master x86 build image that can be automatically upgraded to amd64 as
needed.  Shops with existing x86 systems that want to upgrade to amd64
hardware can copy the existing install to new hardware, upgrade
in-place, and be done with it.  Shops with hardware at remote sites
can upgrade in-place.

Thanks!

- Morty