Modding classic iPods is such an awesome rabbit Hole. You can exchange the mini hard drive with anything from regular SD cards to quad micro-SD cards to even MSATA and M.2 SSDs. This also creates extra room to install a giant battery if you want to.
I am currently trying to find a way to embed a Bluetooth transmitter so I can use my Bluetooth headphones with it.
There's even an alternative firmware called Rockbox that allows you to just plug in the iPod using USB and put MP3s on it instead of using iTunes.
I also own a Creative Zen Vision but it's sadly not as customizable and there's no Rockbox firmware for it.
Edit: before posting I didn't see the link to the original post which talks about most of the above.