I ran across this site recently, and despite some spelling errors, it has an awesome collection of videogame console concept art and unreleased consoles. It’s worth it just to see what the SegaCD almost looked like.
https://sites.google.com/site/virgingamernews/unrealsred-consoles
The Sega Cd on that site is really awesome. However its not an early design idea its an actual Dev Kit. The version developers use when creating games.