Ability to add and remove multiple points
It should be possible to add an array with addPoint() or better to have addPoints(), insertPoints() or addData() where 1) array can be given as argument, 2) insertion index can be given as argument in case the data is already sorted. Or maybe have ability to splice new array to existing series.
More info in related GitHub issue: https://github.com/highcharts/highcharts/issues/4724
I'dsay that it would be nice to have it, as long as it provides some performance boost.