I don't know if you answered my question: what is 3D Touch? Sure, it might be convenient, but it's hard for me to imagine without knowing what it is.

> What trackballs offer free scrolling? My trackball (Marble Trackball from Logitech) offers it, with a little configuration. Effectively, you're holding down a button and using the ball as a scroll wheel, letting you move left and right. I can imagine that any trackball (since by nature they have the "ball") with some configuration could be used for free scrolling (at least, well, on Linux).

> And something done with a keyboard is by definition something not done with a mouse. We scroll on a mouse. We can also scroll on a keyboard (with arrow keys). So they are interchangeable sometimes. I know Windows also has a feature to emulate the mouse with arrow keys. So this isn't inherently true, unless I'm misunderstanding.