Replying to zmike:
already implemented: use quickaccess module
I am not sure how this shall work. I imagine, I can autostart one instance of Terminology on E17 startup. I managed to setup a quickaccess key (F12) for an existing Terminology window. But when I close that window and start a new instance, the quickaccess seems gone. Also I cannot start a new instance by pressing the quickaccess key, in case no instance is currently running. In addition to that, the window appears in the window list, Alt+Tab switcher, etc.
What I expect: Quakology (the hypothetical Quake-style Terminology) is autostarted when E17 starts. It provides one window (the rest can be done with tmux or screen) without decorations (they are not necessary) with predefined alignment (always at the top edge), covering a predefined amount of screen space (i.e. 80%, counting from the top edge), which is hidden by default. When I press F12, the window is shown and raised above all others. Preferably with a nice slide animation. Pressing F12 again hides it - even from the Alt+Tab window switcher, so that it does not clutter anything. In addition it has a background of configurable transparency.