Tell Apple what you found, if the BETA has some feedback system or use the Apple.com/Feedback website.
They probably want to remove it since Apple considers a disc legacy/skeuomorph.
That's a strange idea
...(not just optical disks)....
(not just optical disks)
Probably just a typo, but disc refers to optical media like a CD or DVD. While disk refers to magnetic media, like a floppy or a hard drive.
An optical (disc) is not the only kind of storage media that would trigger the "eject" icon.
Yep, that's exactly right, too. Other forms of media, like external HDD's, SSD's and flash drives make use of the Eject button.
Out of curiosity how do you get it to show?