The Lumia 1520's specs are great, but the design is something that's obsolete now. Starting with the Lumia Icon earlier this year, they changed the design of the Lumia. And with the Lumia 930 taking away Verizon branding and introducing new colors, it is carrying on this new design. The silver band around the device is very nice, no other Lumia carries that.
If you saw the leaked pictures of the Lumia 830, it carries the same silver band around the device, similar new back plate. It is something to appreciate, they are starting a newer design similar to the Surface or the iPhone, they've carried the same predictable design since the N9, and while it worked well on that phone, their Lumias have looked fat because of it, for example the Lumia 920.
I have the Lumia 1520 now, but as soon as I can get my hands on a new Lumia with this new design, I don't care if the specs aren't better, as long as it specs equal to or greater than the 1520, minus the 6 inch screen, I'd rather have a 5 inch screen considering the store apps aren't optimized for it quite yet, then I'd go and trade mine in.