I think you got it a bit wrong
Fermi = 40nm
Kepler = 28nm
Fermi cannot be based on 28nm since 40 nm != 28nm
I actually highly doubt that there will be another release at this point.
Nvidia has saved huge amounts of financial funds in the creation and production of the GTX 590.
I donÂ´t think that they could afford to develope card other than Kepler right now because I am sure their funding is highly occupied by the development of Kepler.
Also it wouldnÂ´t be a very clever move from the marketing point of view because customers would only be confused in my oppinion.
Kepler will hopefull ybe released in summer...many rumors say it will.