SD cards can die also.
And, they are not difficult to lose. (The voice of experience...)
Of course, a small case the size of a DVD "jewel box" could hold a hold lot of them...
If Apple does drop the DVD reader/burner, I suppose they could offer a USB external along with the MBs -- plus some nifty sort of SD card "caddy"...
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Without realizing it, we have arrived at the time where Star Trek's pocketable, transportable "Data Crystal" is not only a reality -- but is becoming commonplace...