Make BulkObservableCollection<T> public to the core .NET Framework
Using WPF and ObservableCollection<T> has serious performance issues if you need to add large sets of collection items at once, which is well known today. Each updated item fires multiple events that have significants performance costs.
There are hundreds, if not thousands, of custom implementations on the net to overcome this problem and that have their own, more or less adventurous, way of adding a new "AddRange()" method that does not fire all those events for each element but only once once at the end up the collection update.
There is already an existing implementation written by Microsoft, the BulkObservableCollection<T> Class. (Documentation here: http://msdn.microsoft.com/en-us/library/dd867973.aspx)
Unfortunately this class seems to be part of an namespace (Microsoft.VisualStudio.Language.Intellisense) that is not intendend for public use.
Obviously, this class solves a problem that thousands of developers have and that is topic of forums, blogs and commity pages like Stack Overflow over and over again.
While it be technically possible to find the assembly Microsoft.VisualStudio.Language.Intellisense from somewhere on my hard disk and reference it in my own projects, or to extract the code somehow, these would definitely be only hacks.
Also, I am not sure if this step would be supported by Microsoft's licenses.
So, please move BulkObservableCollection<T> into the publicly available SDK.
Then we all can use it and can stop implementing error prone custom solutions for things that are already solved - which to my understanding is the idea of using a framework at all.