Bump: Two GUI editors come to mind: Tea and Geany.
I think TEA is about as close to your wish as you are going to get. TEA will likely do 95% of your wishes except exit+save and ESC key in sequences. It is hackable and readable Qt/C++ so you can patch and push with ease.
"TEA is a C++, Qt(4,5,6) text editor with the hundreds of features for Linux, *BSD, Mac, Windows, OS/2 and Haiku."
TEA text editor has endless configuration options including all the key mappings that allows custom setting of everything in the KEYBOARD tab as shown in the screenshot. Please note that the quirky monspace font is not the default TEA setting but from my own custom QT settings. You can apply any font you wish to the interface.
If you want to modify hotkeys via source code you would use Qt::QAction in tea.cpp in the repo. I'm not a Qt/C++ programmer but the source syntax is obvious and I have hacked other Qt interfaces to my liking with no problems.
One rough edge I found is that if the application is already open, passing a file via command line will not open it. I could not find any other UX bugs in it.