Once every seat in E- has been purchased on a flight, do non-elites who subsequently purchase a ticket on the flight automatically get a seat in E+? Or do they get "airport check-in required"? (in which case you'd still likely get a seat in E+ unless there are E- no-shows?)

Also, if you have a seat in E- and you're not elite, would a gate agent be willing to move you to E+ if you ask them nicely (and neither E- nor E+ is full)?

Thanks for any info.