In the state of Nevada, the big driving force for any criminal legislation, or in this case long gun registration, will be the Las Vegas Metropolitan Police Department (LVMPD). In my research, in the past, any proposed legislation has to be presented as a solution to a problem.
That said, one would have to analyze the crime situation in the Las Vegas Valley to determine if the there is a critical criminal misuse of long guns (a problem); if so, then LVMPD would have the argument to the state legislature to allow long gun registration (the solution).
Have just lived in Las Vegas for the last seven years, I did not notice the overwhelming criminal abuse of long guns to justify the registration thereof. Perhaps LVMPD could make the argument that the current handgun registration (Blue Card) system is effective in tracking stolen handguns and monitoring the sale or transfer handguns; and therefore, this crime fighting effectiveness needs to be, or should be, applied to long guns.
A big red flag for long gun registration would be open talk by the police department administrators or politicians suggesting or wishing for such authority. So far, I have not seen Sheriff Young or Mayor Goodman, or the Clark County Commissioners state any desire for long gun registration (unless I have missed something).