+1 on this 🙂
Referencing data already on our web server would be great, since we're not using AGO for data hosting. We already have our own open data catalog in place, but it lacks the multiple format download options of open data. I'm actually working on a rolling 180 day crime export right now (csv with lat/long), and it would be great to upload this to our web server and have it published to open data.
I imagine for others direct upload of csv (with an associated tool/arcpy element) to hosted AGO would be useful, plus as you mentioned upload from ESRI Maps for Office.
Nate