The 3.5mm headphone jack is an accepted industry standard for audio output devices and unlike previous instances of connection interfaces and devices being superseded (SCSI, COM, Floppy Disk) it isn't like a newer connector offers any bandwidth, performance or quality improvements over the standard already in place. Audio is analog by nature, whether the output from the Lightning connector is digital or not makes no difference. It still has to convert to analog somewhere along the chain.
A common claim is that an improvement could be made when it comes to durability. However it isn't as though we have widespread issues with the 3.5mm connector as-is, with the exception of some of the dollar store specials that use the cheapest, nastiest built connectors money can buy. I don't believe moving to Lightning connectors would resolve this issue either, based solely on the fact I can walk into Kmart and purchase an off-brand lightning cable that doesn't correctly fit the connector on my iPhone 5C.
So what reason does that leave. A thinner device? A waterproof connector? The iPhone is already ridiculously thin, second only in Apple's product lineup to the iPod touch which in itself contains a standard headphone jack. Once the form or appearance of a device starts dictating the removal of some fairly useful components, I think that's where someone needs to draw the line. Cue everyone that complained about the protruding camera on the iPhone 6. Whether the device is waterproof or water resistant remains somewhat of a moot point as long as the device retains its multiple other points of entry, including the removable SIM tray, which I should mention contains a warranty-voiding liquid contact indicator while the headphone jack currently contains none.
Don't even suggest that removing this supposedly unnecessary component would result in cost savings that would then be passed on to the consumer either. No chance in hell.
So the obvious benefit here lies directly with Apple. For every iPhone they sell, another set of Beats headphones with a built-in Lightning connector goes out the door. For every customer that buys a different brand of headphones, Apple receives a licensing fee through the Made For iPhone (MFi) program, and for every customer that chooses to use a set of standard 3.5mm equipped headphones, Apple makes a sale on another most likely expensive adapter.
I remember using Motorola, Samsung and other manufacturers phones in the past, each with proprietary headphone connectors, each with an optional adapter to adapt them to the standard 3.5mm jack. I rejoiced when the industry finally standardised on the 3.5mm connector. Finally, I could use the same set of headphones with my phone, my iPod, my computer and just about everything else. I could purchase any set of headphones I wanted without worrying about attempting to find a set I liked that also happened to use the same connector as my devices. Now, I can't imagine why anyone would consider a return to every manufacturer having their own proprietary connector a good thing, optional adapters be damned. Alas, that's where I fear we're headed should this rumour be true.
Perhaps Bluetooth will offer a viable alternative to the venerable old headphone jack. Another expensive device with an internal battery that needs to be constantly charged and will inevitably become useless as soon as the battery starts to degrade.