Traditional CAD packages, like Autocad, are co-ordinate orientated ad what you are suggesting is relatively easy to implement. Solvespace is Parametric orientated, using relationships between entities like parallel, same length etc. This is much less suited to keyboard input, but also when used properly makes for a drawing that is much more easily modified. Also, this involves a different approach to drawing, where rather than crating a drawing accurately during entry, in Solvespace, create a rough sketch, and then constrain it to get the desired result. The keyboard shortcut provided for creating entities and adding constraints generaly allow one hand for the mouse and one for the keyboard.