I'm also unsure as to how much would be gained by doing this. Lightest weight launcher, with a single home page with music widget controls seems the same thing.
- If all you're doing is using it for music, it doesn't really need much RAM. It's a background process with the screen off most of the time.
- If it doesn't have a SIM or even just in airplane mode, the phone/SMS capability is already removed, regardless of what's in the ROM. Any other apps which require an internet or network connection will just lie dormant. I agree removing them removes any possibility of battery usage, but they won't 'drain' it significantly by merely existing. For instance SMS won't use anything without a SIM. If you don't login to any gmail account etc, there's nothing to sync, so no usage there either.
- I was always the same, removing unncessary apps and sounds etc from /system to fit it into a smaller hboot. However this was in order to conversely gain as much space on /data to increase space for apps. If the ROM is only used for music, it will have lots of free space anyway, whether it's on /system or /data doesn't really matter in this instance. All the music is stored and played from the sdcard anyway
However if you've already done it and gone through all the effort of stripping everything out of a ROM.zip, why not repackage your own music ROM with only the music player, and release it giving proper credits?
I say put it out there, let the 'market' decide whether it is popular
that's what the development section does