It would be awesome to have a trigger for double tap and move.
Here's the sequence of actions to trigger it:
- Tap trackpad once (tap down + tap up)
- Put finger on trackpad again (tap down)
- Start moving finger without lifting it on a second tap.
As you move finger up/down (or left/right) on a second tap, some action may called continuously, for example zoom a page in/out, or scroll a page.
Reference: On phones, many apps support one-finger zooming using such a gesture.