Check out this homebrew team. They even make their own version of a HUCard.

http://www.aetherbyte.com/aetherbyte-software.html

Finally got to see the internals of a HUCard http://www.romhacking.net/forum/index.php?topic=14103.0

Brilliant form factor.

Haha thanks man. I was really just venting some childhood bitterness from over 20 years ago when all my friends got Sega Genesis and I felt left out with my abandoned Turbografx-16. Appreciate it though.

You're probably aware of this, but the PC-Engine (TurboGrafx's Japanese counterpart) actually did very well in Japan, beating the Mega Drive for second place in that market.