The purpose of weekly lockouts is basically to prevent players from themselves, so they don't grind everything immediately and then complain there's nothing left to do. It's also valuable for more casual players so they know they don't need to play the game full time to keep up with the Joneses. That said, I don't think it would hurt to have a cumulative lockout system of some kind, so if someone leaves for a few months they could catch up with everyone else. I don't know exactly what that would look like, but it doesn't interfere (much) with the good that weekly lockouts do.