You must have seen the same thing I saw at the AT&T store today; the new green 1520 and the new "Cortana display":
I played with it for a few minutes. Exact same thing as any other 1520 except for the color. I was surprised though, as it seemed to be the ONLY Windows Phone they had on display or for sale, one, and two, they weren't advertising "Windows Phone 8.1" at all! Other than the "Cortana" theme of the display, there was no indication that this new green Windows Phone had a whole new operating system on it or anything... just "Nokia Lumia 1520".
Between AT&T and Microsoft, their marketing strategies always seem to leave me scratching my head. They gave up on the 1020's camera tech to sell phones, with the 1020 camera demo display (the tiny plastic scene in a bubble and a dark box to take demo pics in) and discontinued the phone. Now they're counting on Cortana to sell? Don't get me wrong, I love Cortana and everything, but you've got to wonder... how many potential customers were directed to Bing searches at that display table?
Anyway, to the OP, the green 1520 (or any 1520) is an awesome phone and still the top dog! I say go for it! I love my black one. Yes, AT&T took out the built in wireless charging and only offers 16GB on board, but both shortcomings can be remedied by adding a wireless charging cover, and a micro SD card. I have a 64GB card in mine, and as long as it's a "class 10" card, it's fast enough where you can't tell the difference between it and onboard storage. (I can't!)