For anyone interested, I built a contraption that can be used with Arduino. It is an I2C keyboard controller made from TI-99/4A matrix keyboard (made by Mitsumi, they were available on e-bay new and cheap some time ago) and AT89S52 (8052 compatible) micro controller. I don't think this qualifies for a Playground/wiki entry, but may give the hobbyists some ideas if they are in possession of a matrix style retro keyboard or a keypad. This project is open and can be adapted to any matrix keyboard by changing the firmware and perhaps few electrical connections to adapt to the specific keyboard connector.
Here is the blog entry:
I hope you find it helpful. Enjoy.