Microsoft's "I mean it" content-type parameter

Hi,

(crossposted to both the HTTPbis WG's and HTML5 WG's mailing lists...)

looking at 
<http://blogs.msdn.com/ie/archive/2008/07/02/ie8-security-part-v-comprehensive-protection.aspx>:

"MIME-Handling: Sniffing Opt-Out

Next, we’ve provided web-applications with the ability to opt-out of 
MIME-sniffing. Sending the new authoritative=true attribute on the 
Content-Type HTTP response header prevents Internet Explorer from 
MIME-sniffing a response away from the declared content-type."

Let's ignore the issue of inventing a new media type parameter for all 
new media types for a moment...

It's good that MS recognizes that content-type-sniffing may be bad and 
that they are doing something about it. But is this really the right 
approach?

BR, Julian