I know a lot of fields have complex symbology they are using for polyline and polygon features, which would be great as web feature services for collaboration.
I have found that this is a major show-stopper for my organisation (85,000 pers) in adopting ArcGIS Online as a mainstream tool in day-to-day planning. We have a team committed to making this work, but without complex symbology drawing options, we are limited in expanding our consumer-base to the bulk of the organisation.
For example, we have line features with triangles, boxes with circles in them and specific markers on the contour lines... all of which are fairly hard to draw on a computer to start with. They also have to made on a map, at certain scales and with coordinate systems. Our current GIS software is dating and only allows GIS users to use it effectively. We now have Portal and ArcGIS Online, but without that final representation, we cannot empower our end-users to conduct the work themselves.