FNG was mooted long time back, in the early 1990s. But then, the 'Eastern Peripheral Expressway' and 'Western Peripheral Expressway' were proposed as a more scientific and futuristic way of connecting the suburbs, and the FNG was shelved.
By that time, FNG had already appeared in the master plans of noida and faridabad and till today, most of these maps mention it. Therefore builders are not exactly wrong when they use this term.
Whether FNG will be pulled out of cold storage, depends on a number of factors. Like the construction of EPE and the Kalindi Bypass and the impact they have on Noida and Faridabad traffic. Both these are currently themselves in limbo and at least 3-5 years away. Only when these get constructed and if Govt. realizes that there still is a need of FNG, will they take it up. Till then it'll only be the NH2 or Kalindi kunj bypass (if constructed) that'll connect Noida and Faridabad. EPE is too far from Faridabad to be used by Faridabad-Noida traffic.
I don't foresee construction of FNG before, say 2022, if at all it is constructed...