Resizing the window containing a CartesianChart with SplineSeries leads to some incorrect rendering between points:
Data can come dynamically from JSON, XML, and SQL. Without the ability to bind a grid to commonly used structures (like a Newtonsoft JSON, .NET DataTable or Dictionary), this grid has VERY limited use for apps that use modern ways of gathering and managing data (like JSON-Schema).
Provide a tabstrip control that allows users to display content on tabs. - Tab content could use virtualization to avoid extra rendering - Follow themes from Telerik
Universal combo box.
Add a setter for the AutoCompleteBox's SelectedItem property.
For example, to use different keys than the default arrow keys to switch from day -> month -> year in DatePicker