Its not just size that matters
Lets get to the root of why perhaps the sales have plummeted.
1. Everybody has a 50" they barely watch because they are either on the internet or tapping on phone to social networks.
2. We got stung, 720 became 1080, became Smart and now 4K with 8K sitting in the wings. seeing as we are mostly doing point 1 above who wants the added expense.
3. Smart and 3D we got just enough to make a buck and nothing more. Post purchase upgrades to the smart or come to that the 3D firmware so confusing or non existant that people cant be bothered with it, most just want to utter the words make it go. And dont get me started on the slow EPGs.
4. Standard is not standard, connect the hdmi from one source to a destination and you might get lucky if its the same brand otherwise suffer in some minor technicality.
5. Interactive TV, multiview and other stuff the promise of blueray. But here we are years later and still not there, just like each mediocre release of games machine with a long list of features that never materialises.
6. And lastly Granny, Grannies got the dosh? but oh my gosh just look at all those buttons, regular calls to the son in law on how to change channels. Let alone when you switch it on and the audio auto configures with the last volume setting blowing poor old gran out of her slippers screaming take it back take it back.
Basically the people have got tired of shelling out for promises in a marketplace where they are not sure the job they have will be compatible with them. So why make the big spend. For a few who will always shell out for bleeding edge tech this may not be a problem but for the gaffaw gaffaw, edge of the crust look at what I got non technical, Next shopping, VW/Audi driving (who nearly always buy panasonic too) otherwise known as the lower think their upper middle class, which accounts for most people that close to the wherewithall to consider the purchase. Well they already have 3 generations of wide screen in their homes and have probably run out of space on the walls unless you can really really convince them its worth it.
Otherwise we would all like that 8ft screen that gives the feeling of immersion, somewhere in the home. But you know what, for a quarter of the cost you can experience the real thing. So for now, 1080p with 5.1 surround, Blueray and 3D is enough. I remember the price point being £400 now its a whopping £800 - 1200 and for that to see the same things I saw for £400 does not make me or probably anyone else feel its VFM.