Almost a year later, so not sure if this is still of interest.
The latest version of MidiFire (2.0) includes the 'KEY' rule in the StreamByter for sending keystrokes from MIDI messages (mac only) to the currently focussed application.
Note, for this to work, the first time a keystroke is issued, macOS will prompt you for permission. If you don't follow the prompt and allow MidiFire to 'control this computer' then no keystrokes will work until permission is granted.
To grant permission manually, open up System Preferences and navigate to 'Security & Privacy' and then the 'Privacy' tab.
Use the '+' button in the 'allow the apps below to control this computer' list to add MidiFire.
Keyboards are a different beast. They are run by iOS as specialised extensions to the operating system itself.
OK thanks, fair enough. A workaround could be to either Frankenstein a Launchpad with the electronics of a Bluetooth remote keyboard, or to map MIDI messages (notes) to screen taps using Accessibility Switch Control, emulating a keyboard.