the support engineer that logged this for you is no longer with us. I tried to find the Feature Request he created in order to determine what has happened to it. But I couldn't find it - it's buried somewhere in your issue tracking system.
Are you aware of the image comparison feature? I think it might be the result of your Feature Request. It works like this: You execute a test with Quick Execution. If a step fails, you can compare how the page looked when you recorded the test and how it looked at the time of execution (see screenshot 1). This is pretty similar to what you're describing but it's images instead of html code.
Check out the feature, if you feel it doesn't cover your needs, then I can log a new Feature Request on your behalf.
Hope to hear from you soon!
All the best,
the Telerik team