I have a branch with an early prototype in the toolkit here: GitHub - Esri/arcgis-toolkit-dotnet at dotMorten/PopupView
I did encounter a couple of minor issues that we fixed for Update 3, so you might see a couple of minor issues with 100.2.1. It also needs some UI love, but it does more or less work.
To answer your question about what the difference is, the way I'd like to think of it is this:
- The PopupDefinition is the description how to display attributes.
- The Popup is the "Model" for a specific feature which combines the Feature and the PopupDefinition.
- The PopupManager is the "ViewModel" for that Model.
- The PopupView in the Toolkit branch above is the View/presenter part for that ViewModel.
The Callout is merely a container synced to a location on the map. It's really just meant for showing a little bit of info, like the title, and can contain a button to open up a popup view/page for editing that features (some popup views are so large they obscure too much of the map). Technically you could put that PopupView inside the callout, but in my experience it isn't as great an experience as navigating to an edit page or opening a side-panel/window with that detailed view in it.
