Well, that would be nice. But I think not. There are several issues...
1) there is so much underlying code that the time line components are very difficult to change. Most changes get clobbered by the code.
2) All date/time info, is contained in the timeline itself. So, all milestones, etc., need to access the timeline. Gluing to span calculator to a milestone creates an extra layer which must be traversed to obtain the timing info. So, the span calculator would have to be altered to read the milestone rather than the timeline.
3) it would take more code to get the span calculator to determine which milestones are to its immediate left/right.
Those are the most obvious problems that would need to be solved.
Wapperdude