Putting the controller on a daughter board let's you use any one you like, and that is a good thing. I also don't want to break the through hole pattern of the project =) And also if the Teensy is discontinued, it's always possible to build something similar yourself. And I don't feel like spending time on building the circuit... And as of now, the interface is by 2 connectors, no soldering the Teensy directly onto the main board.
Here is a proof of concept driving 24 columns with only 5 outputs
Not a valid vimeo URL
If there is logic for 24 columns, why not make it 24 columns?...