Audiophiles over the years have had to cope with some highly disruptive new technologies. First there was the wax cylinders, then 78's then LPs, then cassettes, then CDs, then DVDs, then SACDs and DVD-As, then streaming...and it keeps going.
Cell phones have also caused some major product disruptions - try to find a new entry-level point-and-shoot camera - with new phones' photographic capabilities approaching that of professional cameras that whole category of products was absorbed into cell phones. And as P&S cameras disappeared, selfie sticks took their place...
And the same thing could happen to stand-alone portable players.
Currently there are several good reasons for employing a portable playback device. The first reason is sound quality. Current generation portable players have better DAC chips and digital sections (they can use components that need more power). They also have better analog circuits and a more purpose-built internal architecture. All this better technology adds up to better sound.
Current generation portable players are also able to drive headphones that many smartphones can't. Portable players have beefier and more refined output sections with lower noise. Also, the top portable players with wireless headphone options employ aptX HD and at least 4.0 BT protocol.
Storage is another area where portable players have an edge over smartphones. Even some of the less expensive portable players can handle large SD memory cards, and every portable player I've seen can take removable storage cards, so that you can easily carry a large library. With Some smartphones you can also use removable memory cards, but one of the most popular ones, the iPhone, lacks this feature.
Battery life can be critical during a long distance trip. Using a portable player means that your smartphone can sleep blissfully in your pocket while your portable player provides tunes. Some of the latest generation of players offer impressive battery life - the latest FIO M3 can deliver 24 hours of playing time! Combine that with one of the new portable back-up power sources and you could go for days without seeing a power source and still have music.
When I travel for work, I always carry redundant back-up systems for critical gear. This probably comes from my years as a commercial photographer. Some portable players have additional features that allow them to perform a number of smartphone functions when connected to a WiFi network. In an emergency, if my phone dies suddenly I can port some of its critical functions to my portable player.
Flexibility is another area where portable players offer some advantages over smartphones - many portable players can also serve as external DACs for computers or streamers.
One last thing that portable players can do better than smart phones - take abuse. I don't mean that portable players are that much better made than smartphones (although some are), but that you can take them into a more hazardous environments and not worry about damaging your electronic lifeline, your phone. Sweat much when you work out? I do. But with a portable player strapped to my arm instead of my phone it doesn't matter how wet it gets or how many times it gets bumped since it is a player, not my precious phone.
But phones keep getting better, more powerful, with greater capabilities. And with point and shoot cameras assimilated, their next target is definitely portable players...
Some of the most recent generation of smartphones have the ability to stream from higher resolution sources. This will eventually become a standard feature on most phones. Also, battery life on new smartphones keeps increasing. Combine that new phone with an external wiredDAC or wireless Bluetooth DAC and you can see how many people will find that they no longer need to own a separate portable player.
When will the end come for portable players? I suspect, just as with photographic gear, the entry-level side of the business will be affected first. But I can see that eventually all portable layers will become redundant as a smartphones absorb them into their Borg-like embrace.