This will not be available until the next core release at the earliest.  Cathal is in charge of this and I am not sure when he will officially commit to it and even then it will probably not be announced with any specific date aside from saying next core release.

And, let me post something more contructive on this thread (my past few posts have not been approved by the moderator, so they probably weren't constructive).

Here is an excellent article from the Microsoft Patterns and Practices guides.

How To: Prevent Cross-Site Scripting in ASP.NET

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnpag2/html/paght000004.asp

Any ASP.NET application that accepts user input and presents user input back out to other users should follow the recommnendations in this article.