[Blue Jays]

That is easily resolved.
If baggage cannot fit in the class where you purchased your ticket, under the aircraft in the cargo hold it goes.
Easy-peasy.

[MortMan]

That requires policing by the airline. Under the current situation, when there is no more room, bags get put in the cargo hold. Under the 1st class-last approach, the last few coach passengers will be staring at open bins (which may or may not be filled, eventually), which is likely to evolve into more incidents.