The system I had in mind was one where guilds could opt in at the start of tiers as a "casual" "semi-casual" "semi-hardcore" or "hardcore" guild. A "casual" guild could raid up to 8 hours a week. A "semi-casual" could raid up to 12 hours; "semi-hardcore" 16 hours; and "hardcore" could raid unlimited hours each week. Then whenever the guild enters a normal or heroic difficulty raid of the current tier, blizzard tracks the hours and minutes and will lock out the guild from the raid for the rest of the week when they reach the limit imposed on their guild classification.
Then, either provide a site for guild rankings or an API feature that would allow sites like wowprogress or wow-heroes to track the rankings of guilds by their classification.
Throughout a tier a guild could opt to go from a more strict to a less strict classification (such as from casual to semi-casual) if they wanted to raid more hours but not the other direction. Players that raided in a ladder guild could only move between two guilds of the same classification or move to a less strict one (casual guild to semi-casual is OK but to go from hardcore to semi-hardcore is not)
Lastly, I would like to see a realm first achievement for each type of raiding classification. Would be cool to see who is the realm's best casual guild and the best semi-casual, etc.