I've been using an HTPC since early 2009.
Welcome to the club.
When you understand what Chromecast is, how it works, and how easily it works - better than your HTPC for the functions it has so far, you're going to wonder why you waited.
The device has essentially one app - an HDTV browser.
It is by every way imaginable a breakthrough technology.
Unlike an HTPC it will not obsolesce over time as Flash and DRM changes. It will never have too little memory.
To say it fails because it only supports Google approved services is like saying that HTPC fails because it needs the internet or that cable fails because it needs a wire or satellite TV fails because it needs outer space.
And unlike those 3 options, the buy-in is $35.
It was developed and brought to market in 2013.
I've met your challenge with a valid answer.
PS - and yes, over the course of nearly 5 years, I have upgraded my HTPC, including full unit replacements to keep up with the times. Yes, I have an HD PVR on it.
PPS - I'd been running OS X, Windows, Linux and Android x86 on the same machine going on 2 years ago.
Not sure why you think that would be a breakthrough.