I´ve been also thinking about TB Display + rMBP, but it´s quite small and even more expensive than TV. If it´s an iMac, then I could live with the 27", ´cause it would be one simple elegant package. But of course I would like a bigger iMac than 27".
But rMBP 15" is just too small for my home use. I like big screens, especially watching movies from one. Of course buying an rMBP would useful also when traveling.
I think you're missing the whole point of Thunderbolt Display.
1. Using 40-50 inch HDTV as a desktop monitor seems pointless. The resolution is low to take any advantage of big space and if you'll have it on the table and sit in front of it your neck is gonna hurt a lot.
2. Why would you want such a huge screen with low (HDTV) resolution? You'll fit much less stuff on it than on your rMBP screen...
The Thunderbolt display is great at 27". It has higher resolution than any HDTV which means you can fit a lot of windows on it. Anything bigger than 30" on your desk is stupid idea, honestly.
My 0.02:
1. For desktop (like working, internet, playing games etc) the thunderbolt display is great.
2. large HDTV is great for movies, playing games... but that's about it. Why don't you buy large HDTV and 3rd gen Apple TV and use Airplay mirroring to wirelessly beam stuff onto HDTV? You can watch movies on the large screen or play games with some wireless bluetooth gamepad. No stupid wires and if you need to be productive, 15" screen with high-res will work much better.
More and more as I read about people getting rMBP I am being amazed. Some people buy this really pricey laptop for movies/internet/games and that doesn't make much sense (not at least now).
If you'd get MBP 15" you could have some cash saved and get the HDTV and Apple TV for it... and I think it'd be enough for you (also the computer is actually the same as rMBP specs wise).
EDIT: re-read your post so I see you havent made the purchase yet, sorry. the end rant is aimed toward general group.