Currently, it's not possible to detect what is going on in the menu (which screen, which item selected, etc.). The only thing a developer can find out is whether the menu in general is active or not.
But I can tell you an undocumented way to find out which menu screen is shown.
0 = main screen
1 = item screen
2 = item target selection
3 = skill screen
4 = skill target selection
5 = teleport screen
6 = equipment screen
7 = end confirmation screen
8 = status screen
9 = party order screen
What's also possible is drawing a custom (maybe even animated) menu background, by handling the onSystemBackgroundDrawn callback.
Also, it's of course possible to draw something on top of the menu, using the normal onFrame callback.
By combining these things it would indeed be possible to add additional stuff to the menu, at least to the main menu screen. Other screens would still be difficult because additional information (which hero is selected, which item is selected, etc.) is not available yet.
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Mir war nichtmal bewusst dass ich nominiert wurde, aber: Cool! Hälfte des Lobes muss aber unbedingt an Archeia!