Hi Wolfie.
The keyboard uses a proprietary serial protocol to communicate with the MCU of the Microsoft gamepad.
The Viking modchip "hacks" the gamepad by attaching directly to digital and analog I/O lines of the circuit board. We don't connect to the serial port lines on the circuit board that ultimately connect to the Microsoft chat pad.
I also looked into designing a rapidfire modchip that would plug into the chat-pad port. However after snooping of the serial port, it was discovered that information pertaining to game button presses are not part of the simple language used on that serial port. It only does the letters. The most somebody could do would be to build a modchip that helps kids trash-talk via text faster.
You can macro text, but, you'd have to always start on the same letter of the Microsoft on-screen keyboard. Ironically, my very first test-run on the macro back in summer 2010 was to have the macro controller spell out my gamertag name of "odingalt"! So long as the on-screen keyboard layout doesn't change, and you start your cursor at the same place, you could create a macro that types out words.