hey
I just can speak for my firmware (neorainbowduino), answers are below:
- scrolling text (marquee) function → see nr3)
- print word (as opposed to single character) function → see nr3)
- whole frame bitmap upload via I2C (as opposed to a row mask) → yes
- support for multiple rainbowduinos/matrices for all of the above? → yes
you can use a simple processing sketch (or eclipse if you want) to send data to the rainbowduinos.