In addition to selecting a keybind function from the binding menu, what about a second option to simply press a key and have it use that? Would work for things that aren't found in the vanilla menu, like Modular Powersuits keybinds.

I'm not familiar with how Modular Powersuits do their keybinds.
I don't see any reason for a mod to not register their keybindings, especially now that Forge allows you to register keybindings with Ctrl and Shift.
If you can give me any example of a 1.10 mod, where this would be useful I will reconsider :)

Another use for this would be hotkeys for multiple functions at once, as if the actual key were being pressed. Like say I have a bunch of mod HUDs toggle visibility with the same key, I can't do the same with MineMenu.