I finally made the big jump, switching both my carrier and my primary device.
VZW -> T-Mobile
GNex -> Moto X (DE)
Especially in the former case, I'm pleasantly surprised. Thus far, I'm actually getting better reception than I did on VZW, though I'm not sure if this has to do with the difference in radios or coverage. I'm still in a period of transition where I have both carriers and phones, so they're pretty much side-by-side until the GV porting goes through. In the primary areas I've traveled so far, the T-Mobile/Moto X device is getting better reception. I was a bit concerned with this, but after reading some input from user
alostpacket, it's good to see that my results were consistent. In the end, I don't really care to know the specifics-- I just like that it works and it's saving me money. I'm fine with that.
On the device end of things, the Moto X is doing what I've expected it to do, pretty much shoring up the weak points of the GNex. It has a leagues better display (including color reproduction at low-light setting, no banding), much louder and higher quality speaker, better radios and reception, much improved battery life (partially due to getting off VZW LTE), and increased memory (I'm running a lot of processes, and this is key to avoiding the OS from task killing). I'm not overly impressed with the camera in low light settings, but I need to look into the software update.
I'm aware that it's still the honeymoon phase, but I actually didn't have any game-breaking issues with my GNex. I wanted essentially the same device, but with the items above addressed, and the Moto X seems to fit that, and then some.