I would imagine most applications would use the Alert, Confim, Prompt concepts so it would be nice if they were built in.
It would further be nice if they were styleable and callable from c# code very similar to the wpf.
Of course as a default they could follow whatever css style is being used already.
RadWindow.Alert(text);
RadWindow.Confirm(text, () => {});
RadWindow.Prompt(text, result => {});
https://docs.telerik.com/devtools/wpf/controls/radwindow/features/predefined-dialogs