I'd like to propose a new trace type, provisionally called fromto, which would be inspired partly by ggplot2's geom_segment (paging @cpsievert!)

The behaviour would be to draw onto cartesian axes a line segment from x/ y to xend/yend (all 4 being data arrays) with the ability to specify what the start/end points look like: arrows, points etc. More advanced variations might include curved lines, or manhattan lines or whatever. We would be able to reuse a lot of pre-existing machinery to do this: lines, points, arrows from annotations etc :)

The use-cases for such a trace-type are multiple:

1. Gantt charts (both for the time-bars and for the dependencies!)
2. Connected dot-plots
3. Quiver plots
4. The 'link' portion of a node-link diagram