Currently, on a chart with multiple series having distinct x values, step lines can look awkward when one series ends before another.

My immediate desire is simply to have an option to extend step lines to the right-hand edge of the chart. It should work when addPoint() is used on another series and the chart is redrawn. That is, all series drawn with the "step" option should be drawn as-if they have an additional point like [chartmaxx, serieslasty].

I don't need full extrapolation capabilities, that is, I'm not asking for any logic to decide how to draw points that might occur in the future. This is merely a presentation issue, so that step lines may be treated as having the last value until the next one arrives.

This was mentioned in a comment on another request, but have a strong desire for the feature and want to make it official. For reference, see Mark Crossley's comment from December 2012 here:
http://highcharts.uservoice.com/forums/55896-general/suggestions/3311322-step-position-on-between-