Absolutely a bad idea. Not everyone in a guild is going to be playing GbG, and some will play at the beginning of each restart, some at the end, some in the middle, and some play a bit here and there throughout the daily session. Your idea is just going to sabatoge those who do not participate at the start of each reset each day. Since attrition is 'player' based, not 'guild' based (as GE is). Last thing anyone wants, as problematic as GbG is right now, is more problems added to it.One siege camp is a good idea but not realistic. More siege camps means more diamonds spent and profit for Inno which is perfectly fine. They need to make money to provide this service. A better solution would be changing the attrition system. Attrirtion increase should be based on the number of players in a guild similar to GE.
If guilds do not truly belong in the Diamond league, then they should go back down a league that they can play in. They want to stubbornly refuse to play the league that they are able to play in, then they can stay in Diamond and just watch the other guild(s) continue to dominate the underpeforming and underserving guilds.