Bug#1128325: dpkg-scanpackages --arch=amd64 should ignore "arch-all" packages

Package: dpkg-dev
Version: 1.23.5
Severity: wishlist

Dear dpkg maintainer,

Running `dpkg-scanpackages --arch=amd64 dir/` generates a Packages file 
that includes both arch-amd64 and arch-all packages.

(This made sense previously because Debian and other derivatives did not 
have a `main/binary-all` binary path, just `main/binary-$arch`. And it 
probably still makes sense until bugs like #915948 [1] are fully resolved.)

However it would be nice to have a way to exclude arch-all packages 
while generating Packages files.

Could `--arch=foo` be modified to mean "strictly foo, without all"? 
Alternatively could a new option like `--arch-strict=foo` be introduced, 
if you believe that the old behavior should not change?

[1] <https://bugs.debian.org/915948>

Regards,