I am 6, not 8.1, but the following can be done.
Ctrl + Shift + N works for files in a project. For files outside the project, there is no Keymap by default. You can install it yourself.
Go to the "Settings" - "Keyboard Main Menu" - "File-Open File ..." section and set it to any key press.
I just tried to open a dialog using only the keyboard, and this is not so bad, you just need to know to stay in the file name field. Therefore, if you want / home / user, then type / home / user and press return, it will change you to this directory. Not as good as good completion in crtl-shift-N, but not unsuitable.