Well I am not sure what is the reason for such a product, would it not be better to use a smartphone to play back music? There are tons of applications to choose from and yes it may be a bit bigger but the functionality would be much more enhanced, e.g. it could also be used as a GPS.

And you get a ton more of storage space too.

As an example, the Redmi 9c would come with 32 GB of storage, has MicroSD expansion capabilities and a huge 5000 mAh battery.

Xiaomi Redmi 9C (32 GB, Twilight Blue, 6.53 ", Dual SIM, 13 Mpx, 4G, 3G, 2G)