There should be the ability to both download charts as a file so they can be used in another game if Rhythm Plus is used for charting, and the ability to share the ability to edit a chart with certain people, so they can also modify the chart as they need and obtain the file themselves.
Thanks for the suggestion, import and export functions as you suggested should be added in the editor soon, and possibly collaboration in the future as well.
There should be the ability to both download charts as a file so they can be used in another game if Rhythm Plus is used for charting, and the ability to share the ability to edit a chart with certain people, so they can also modify the chart as they need and obtain the file themselves.