The control should be customizable so you can place also a content different than an image as in the WPF native splash screen support (https://docs.microsoft.com/en-us/dotnet/framework/wpf/app-development/how-to-add-a-splash-screen-to-a-wpf-application).
Implement UI for hiding sheet. The sheets can be visible, hidden, or very hidden (could be made visible only from the API). Note: This is already supported on model level (in RadSpreadProcessing).
Implement support for content controls (a.k.a. Structured document tags), which will allow inserting editing controls in the document: - Rich Text - Plain Text - Check Box - Combo Box - Drop-down list - Date picker Do not confuse this feature with form fields support (see http://feedback.telerik.com/Project/143/Feedback/Details/146869 ).
Add a feature that allows you to open a sub menu when you click on a RadNavigationViewItem.
Similar to the hamburger menu in the Windows' Mail application.
allow user to set TimeSpan in RadTimeSpanPicker from text input
Currently when you have null value in a cell, RadPivotGrid considers it as 0. This way when you apply some Aggregate Functions, like Average for example, the result may not be as expected. For example if you have the cells 10, null, 10 RadPivotGrid will show as total the value 6.67 (for Average function). You should be able to exclude null values, so the value 10 will be shown as average for the mentioned cells. Available in the 2016 R2 release.
Want to add multiple Buttons/Commands without changing whole style.