In the end I guess it depends on how you sit on your couch, but AFAIK the ergonomic guideline would be that your eyeline should be aligned to the top of the display.
Meaning that, if you're sitting on your couch, you're sitting slightly reclined, and the eyeline would be angled upwards. That's why you often seen the rule of thumb for home theaters "eye height = middle (or even lower third) of TV".
Incidentally - that's how I've rearranged my own viewing arrangement recently (raised the TV for ~20cm to make room for a well-positioned center speaker), and while being skeptical myself in the beginning, it has worked out great.
But yeah, TV over the fireplace is still terrible. :)
I think it ultimately depends on the individual situation and layout. We had our last TV over the fireplace for 12 years. Our seating was ~15 feet away, and we did not need to crank our necks to watch TV.
I think I'd be much more critical of those things if I was 20+ years younger, when I was more into "home theater" than I am now, but my attiude nowadays is "if it works for you, who cares what other people think."
We had an LCD TV over our fireplace (gas, vented directly outside horizontally) for 12 years. While it just got moved in the past month, it's still going strong.
I've seen countless HGTV make-overs where they put the TV other the freaking fireplace - just horrible. This is slightly better, but still bad.
The idea is simple and not actually new; I saw a similar idea years ago where instead of a home office it enclosed a small bedroom with bunk bed. It seems it wouldn't be that hard to replicate for anyone able to make their own shelves.