This project has been in the back of my mind since the bush administration. Thanks to some very bad typing habits I have mild carpal tunnel syndrome in my right hand. My left hand has been spared so the idea of having a keyboard that can offload the work to the undamaged hand is a compelling one.
The main problem with most one-handed chorded keyboards is the lack of a way to move a mouse. Most designs (including the original Engelbart model from the Mother of All Demos) assume one hand for the keyer and one hand for the mouse. Both are less useful for people who only want to use one hand for both or be using the keyer to control a mobile platform.
The first idea was a simple one; Add a thumbstick like you find on modern game controllers and have that be used to control the mouse. The second idea is the big one. The mouse thumbstick is not in use while typing, and the more keys added to the keyer the greater complexity both in the chords and in the construction. Instead of having a large number of keys and combinations or a small number of keys and the requirement for multiple keystrokes to type lesser used symbols the thumbstick can, in typing mode, be used as an additional set of shift bits to allow other symbols, numbers or control keys to be accessed. This allows some chords to be reused in an easily memorized way, shift-space is tab, shift-delete is backspace, etc.
People who, like me, have carpal in one hand and not the other or limited mobility in their hands can also benefit. The travel distance for a chorded keyboard is significantly less than for a conventional keyboard and using low force switches you can have minimal force for nerve-damaged hands while still having an audiable "click" for feedback.