Adrian,
I would like to see the ability to select a feature, click a button that says "Copy Shape", then select the feature class I want to add it to. This works great in Collector but I've yet to figure out how to replicate it in a web app.
For instance, I put together a web map for Collector where our field crew can select a stand, click copy shape, and add the shape as a new feature in another polygon layer. See pics below for what I'm talking about.