This is a difficult one so apologies ahead of time.  The following piece of code works in v4, but not v6 inside an HttpModule.

ResponseCaptureStream filter = app.Response.Filter as ResponseCaptureStream;              

if (filter != null)
{
  //filter is null for v6 not v4.
}

The main differences I can find between v4 and v6 is the output filtering is the filter type: 

In v4 the type is: System.Web.HttpResponseStreamFilterSink

In v6 the type is: ClientDependency.Core.Module.ResponseFilterStream

In v6, 'filter' is null because it fails a cast.

What I'm truly after is the final HTML on every request.  I don't actually need to perform my own filtering.  Any suggestions on how to read the stream?

The ResponseCaptureStream class is as follows:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Text;
using System.IO;

namespace FastCache
{
    public class ResponseCaptureStream : Stream
    {
        private readonly Stream _streamToCapture;
        private readonly Encoding _responseEncoding;

        private string _streamContent;
        public string StreamContent
        {
            get { return _streamContent; }
            private set
            {
                _streamContent = value;
            }
        }

        public ResponseCaptureStream(Stream streamToCapture, Encoding responseEncoding)
        {
            _responseEncoding = responseEncoding;
            _streamToCapture = streamToCapture;
        }

        public override bool CanRead
        {
            get { return _streamToCapture.CanRead; }
        }

        public override bool CanSeek
        {
            get { return _streamToCapture.CanSeek; }
        }

        public override bool CanWrite
        {
            get { return _streamToCapture.CanWrite; }
        }

        public override void Flush()
        {
            _streamToCapture.Flush();
        }

        public override long Length
        {
            get { return _streamToCapture.Length; }
        }

        public override long Position
        {
            get
            {
                return _streamToCapture.Position;
            }
            set
            {
                _streamToCapture.Position = value;
            }
        }

        public override int Read(byte[] buffer, int offset, int count)
        {
            return _streamToCapture.Read(buffer, offset, count);
        }

        public override long Seek(long offset, SeekOrigin origin)
        {
            return _streamToCapture.Seek(offset, origin);
        }

        public override void SetLength(long value)
        {
            _streamToCapture.SetLength(value);
        }

        public override void Write(byte[] buffer, int offset, int count)
        {
            _streamContent += _responseEncoding.GetString(buffer);
            _streamToCapture.Write(buffer, offset, count);
        }

        public override void Close()
        {
            _streamToCapture.Close();
            base.Close();
        }
    }

}

I have tried to simply extend the ClientDependency class to no avail.