you could use a smart watch, not nearly as much storage but for playing music while running it can work well enough.

There's a case [1] for the Apple Watch that turns it into an 'iPod'. It's also quite similar to the Pod Case concept [2].

[1] https://thetinypod.com

[2] https://www.behance.net/gallery/72386255/Pod-Case-for-Apple-...