Keybindings are a linear search through the list, whilst adding each additional one is immaterial, if each one isn't actively challenged then they keep adding until keyboard operation becomes slow.
Since nobody has complained about zoom out lets leave it out for now.
because nano...
Geany isn't Nano, if a nanoist wants to change their keybinding thats fine, but its not up to Geany to provide equivalences for every editor out there, thats plugin territory, [see](https://plugins.geany.org/vimode.html)