keyboard

physical properties

Careful attention is given to the location/arrangement/behaviour of the keys. The keyboard provides a precision interface for the hands, similar to a musical instrument.

adjustable to accommodate the kinesiology of many different hands
curved rails run parallel to each finger
the rails swing and pivot under the base knuckles
the keys may be fixed anywhere along the rails
physically symmetrical (not biased for a dominant hand)
keys are coloured but otherwise unmarked (all keymaps remain ready for immediate display)

actuators

All actuators provide as much sensitivity/resolution and separate sample streams as possible which may be filtered in various ways.

keys: velocity and pressure sensitive (similar to a MIDI keyboard)
ball: high-density/massive (for inertia) precision track ball (may be filtered to only register horizontal motion, &c.)
wheel: high-density/massive (for inertia) rotary detent switch (detent mechanism may be disengaged)
joystick: pressure sensitive, natural resistance (similar to Clavia's Pitch Stick found on its Nord MIDI controllers)

ternary modifier keys

It seems preferable to have a small number of well-placed keys and many modifiers, rather than many awkward keys and few modifiers.

2 ternary (neutral/forward/back) switches (per side) provide 9 (3²) keymaps
bicolour LEDs provide visual indication of state (green/red)
any state/keymap may be locked (like caps/num lock)

keymap

It seems reasonable and prudent to maintain a buffer of keyboard input (a keystroke recorder). Among other uses, this data may feed algorithms which perform character/substring frequency analysis (and other such statistics), the results of which may be used to optimise the keymaps (keyboard layout).

The keymaps remain immediately available for display on screen when called. The physical keys may be grouped by colour, though it seems preferable that they are not permanently imprinted with specific glyphs/symbols.