Here are some news.
I merged several repositories into a single one to achieve the generic firmware organization. The new repository is here https://github.com/OpenStoryTeller/software
The target Arduino MKR Zero is now integrated in the build system, it is the second architecture supported after the Longan Nano. Currently SD Card and display are functional (using ST7789 display driver).
In the next step, my goal is to add some buttons, and especially a rotary encoder. Then, the sound!