There will be at least 7 unused pins on the Teensy after completelly wiring the sensor/buttons/LED, meaning, with proper matrixing the firmware should be capable of at least extra... 50 buttons
Its all good on the paper but trying to add a mere 10 could generate lots of problems.
Im not gonna mention much about software which im not good at but hardware, having everything move as it is right now, adding extra 10 buttons is gonna be a major challenge, some of the flexibility is gonna be lost, buttons cant be as big as the left/mid/right and so on.
Im gonna mention some features, these are just ideas, some are harder some are easier to implement, please dont take it as "must do this"
What I`d like to have:
a. 1 button instead of 2 to switch DPI, have 3 presets, pressing the button will cycle those. The way it is right now, the user must hold one of the buttons down while plugging in the cable/teensy to switch to a lower/higher DPI, althought I dont find myself switching DPI all the time I find it inconvenient.
b. ALT + arrow left (back)
c. ALT + arrow right (forward)
d. F5 (Refresh)
e. ESC (Stop)
f. CTRL + Page up (Next tab)
g. CTRL + Page down (Previous tab)
h. CTRL + T (New tab)
i. Minimize active window
j. Minimize all windows (Show desktop)
I guess these cant be done unless you have a Teensy 2.0 so you can test/debug.
Next amazing thing would be a GUI to switch buttons profile from let say "Navigator" to "Video editor" and have shortcuts like CTRL + arrow left, home, shift + home, del, etc, and "Coder" - Insert tag, save, switch tab, etc... but we long way from this if will ever get done by the community.
After re-designing the top cover for the sensor I`ll get printing the parts for you, thanks for everything @nevin.