[arch-general] How to detect when a package is removed from a group in pacman

[F B]

Hi,
recently bin86 was removed from base-devel group but the unique way I know to see this change is manually reading the pkg changelog in the arch site.
The problem is simple, how to detect this change in pacman?
For example, after a gnome upgrade, if a new package is added to gnome group I can do:
pacman -S --needed gnome
to install the missing package.
But if a package is removed? How can I remove this package that doesn't belong to a group anymore?
I hope you understand the question.
Why not add metapackages (as for kde) for base, base-devel, gnome and gnome-extra that doesn't have this problem?