Killing the floppy - Pathetically small and slow storage that was more or less useless by standards even at that time.
Killing Serial/Parallel/ADB ports - USB had plug and play while the machine is on, zero configuration, and it was an emerging universal standard.
Killing flash - Buggy, slow, insecure, battery killer, web standards emerging to replace it.
Killing the optical drive - Few people were using it anymore, took up a third of the space inside a laptop.
Killing the 3.5mm audio jack - ...thinner?
Stupid, stupid, stupid decision. People use the audio jack every day. There's nothing newer to replace it that doesn't require an external DAC. It's not buggy or insecure. Aside from reclaiming a tiny bit of space inside, there's no good reason to take it out. And I'm all for getting rid of legacy stuff.
It's worth pointing out that even when Apple "killed" the optical drive, they only dropped it at first in a single niche, expensive laptop in 2008. Every MacBook, MacBook Pro, and iMac still had an optical drive until 2012. That's a four year transition period, because they thought in 2008 that ditching it was the future but it wasn't really there just yet. They didn't take that risk on their most popular flagship Macs for a reason.