DX will never equal FX. If you have a good quality DX sensor, you can make an FX sensor with better ISO/DR with the same resolution, or have higher MP for the save ISO/DR. In addition, there are other qualities of FX which can never really be acheieved on DX- smaller DoF, bigger and brighter viewfinders, overall better optical quality (since you are not relying as much on a small area of the lens), and you have more options for fast wide angles (there is still no equivalent to the 14-24, 24/1.4 on DX)
However, likewise, FX will never equal DX. For every long FX lens, it is 50% longer on DX with the same maximum aperture, and you get more DoF at the same aperture so you don't have to stop down as much to get more things in focus. Likewise, for every cheap FX sensor, you can make 2 cheaper and smaller DX sensors, and DX cameras use smaller mirror boxes and viewfinders, so DX cameras will always be cheaper, smaller and lighter.
Really, I think the question to be rephrased to DX being "good enough" that a move to FX no is no longer needed. That really depends on what you need a move to FX for. If it's just for high ISO, the D7000 is getting very close to the practical needs (ISO 6400 allows us to use slow lenses in low light hand held). Similarly, if we need high moderately resolution, the D7000 is pretty good at that already. For the more demanding of us, FX delivers even better results. On the other hand, if you need an advantage inherent to one format or the other, then there is no real substitute.