Have "molecular clusters" for azeotropes been identified?
No, in the absence of extra data, there is no reason to suppose that there is any vapor-phase cluster formation.  

Cluster formation in the gas phase would demand very, very strong departures from ideal-gas behavior.  To the contrary, the ideal gas law is an excellent descriptor of gas phase mixtures of ethanol and water.

Check out a Wolfram Demonstration for the ethanol-water system.  It says:


  You can vary the pressure $P$ to any value between 50 kPa and 200 kPa  (i.e., low to moderate pressure so that the ideal gas-phase assumption holds).


If the ideal-gas assumption holds, then there is no significant structure formation in the vapor phase.  The "ideal" gas law describes negligibly small particles that have no attraction or repulsion to each other.  Structure formation means that molecules must be strongly attracted to each other in order for arrangement into a persistent structure to occur.

An "extended" form of Raoult's law that is valid for non-ideal vapor as well as non-ideal liquids, and thus is applicable to azeotropes, is 

$y_i \phi_iP = x_i \gamma_i p_{i, \mathrm{sat}^{\star}}$ 

Here, $\phi_i$ is the fugacity coefficient and takes into account vapor-phase non-idealities (i.e. deviations from the ideal gas law), and $\gamma_i$ is an activity coefficient and  takes into account liquid-phase non-idealities.  

For many, many systems of interest, $\gamma_i$ is the driver of non-ideality, including azeotropic behavior.  Fugacity coefficients $\phi_i$ are negligible (except at enormous pressures) a much higher percentage of the time than activity coefficients $\gamma_i$.  This is because liquid phases are often far more dense than vapor phases, meaning that intermolecular forces govern behavior to a much stronger degree than in vapors.