So what you are saying is lets say you booked the reservation 3-6 months in advance or even 330 days in advance you could be booted back to Y. Wouldn't they boot the last one who booked First Class on an upgrade or lower fare base plus status with Delta?

Shouldn't there be a reason for the boot like a letter that Due to unforeseen circumstances we regretfully had to downgrade you back to Economy. There should be some service recovery like refund of miles or Cash and a Voucher to use to be upgraded again for your next trip on Delta(with little to no restrictions) and of course include food and the alcoholic beverages as part of the downgrade.