Just imagine if you will: Instead of auto-ejecting a window pops up on the screen of the Macintosh when it's done with a disk and instructs the user to "Please remove disk from floppy drive #1".
(I know, it's a stretch, but isn't it awesome? With that one simple suggestion I've just cut the price of the Macintosh drive mechanism significantly. Now if we ditch that silly auto-inject system we can *really* start saving some money...)
Add a fifty cent microswitch and a "disk present" sense line to their already custom drive controller board?
Just to clarify, Burrell Smith didn't design the Sony 3 1/2 inch *drive*. He may of had a hand in the modifications that Apple put into the custom version they had made for the Macintosh but he by no means designed *the drive*. (The first Sony 3 1/2 drives hit the market in 1981 and companies like HP had used them for several years before Apple discovered them.) Here's folklore.org's take on the adoption of the Sony drive over the Twiggy.
As to using the Apple ][ 5 1/4 inch disk drive very early Macintosh prototypes used them, but I suspect "prototype" in this context means "circuit card screwed to a board". Color me skeptical that they ever made any "real" cases incorporating them, but it is of course very possible that the Appledesign concept sketch you linked in dates to an era where Apple ][-drive utilizing prototypes were what was floating around the office. (Thus making it perfectly logical for the artists/draftsmen to use them as component references when spitting out design drafts.)