It would be useful if you could select multiple datasets from ArcGIS Open Data and add it into a webmap to compare datasets.
At the moment, you can only add one layer into a web map, if you need to add more layers you need to save the web map, then search for more layers via "Add > Search for" . There is no way to add in additional datasets to the same webmap via the an ArcGIS Open Data Portal.
Implementing this would allow for a much more streamlined workflow.