This is an extension to ReleasePerSubsystem. Additional to that:

• Multiple versions of subsystems are allowed. E.g. Gnome 2.6 and Gnome 2.8
• Subsysten has dependencies to other subsystems. E.g. Gnome 2.6 depends on X11 4.3
• Circular dependencies are not allowed. Split up subsystems to avoid circles.
• A debian release is a choice of subsystems. E.g. X11 4.3 and Gnome 2.8 and ..
• Security team only provides updates for the debian release.

Pros:

• We can stabilize one subsystem version and work on the next version at the same time.
• Release manager can postpone choice of version until the release (eg. whether Gnome 2.8 is ready for release or not)
• We could exclude a subsystem for some archs if there is no need for it (e.g arm might not need KDE). This would remove load from the buildds.
• We could make a new small release where just choose new subsystems for the desktop stuff while we leave the rest untouched. This way the server admins don't have to worry about upgrades but desktops are still up to date.
• Security team is not overloaded.
• Joe User uses normal debian release. Experts can choose newer version of a subsystem if subsystem developer provides it. E.g. KDE team could backport KDE 3.4 for sarge.

Cons:

• Bug tracking needs to be aware of subsystem version (same package may behave differently in two subsystem versions)

Most of the pros and cons of ReleasePerSubsystem apply here, too.

See ReleaseProposals for alternatives.