The proposed solution is not conventional, but well done for your creativity - it may work amazingly well or fail miserably, like any other novel invention.
I believe others will provide opinions against it, so allow me to focus on the for.
It could actually be an extremely usable UX pattern
Personally, I find little usability in the abode toolbars, like that of photoshop:
It has lots of icons, and an hierarchy of tools (so a long click reveal other tools. I always thought that a more usable solution would be upon pressing some key, a mega menu will appear, neatly organising the tools into coherent hierarchy. Something like in this mega menu, just with the tool names instead of a shortcuts:
In fact, a highly popular Mac application called CheatSheet does something very similar with a keyboard shortcut:
The solution is already a convention, just in a smaller format
The context menu (right click menu) is very similar in nature to what you offer:
It may be right for 100 items as well
Presenting a user with 100 items is dubious and potentially overwhelming. There are a few prerequisites though in order for it to be justified:
- Terms has to be extremely short (1 or 2 words)
- There shall be some division into logical categories, possibly 3 level hierarchy.
- The terms shall be absolutely clear to users so they can find the item quickly without having to think what each item actually mean.
Quite a few mega menus can easily get to 50 or more items. The following example from Ebuyer is fairly good as the terms and categories should be clear to most people (this menu has in total 60 labels):
A bad mega menu is one where users are unfamiliar with the terms, like this Royal Mail menu that despite having less labels (38 in total), is far less usable than the Ebuyer one above:
For instance, users won't know what "Special delivery guaranteed" mean and there is a big mix up between classes here (actions mixed with nouns and a lot of cryptic labels).