The mexican ministry of transportation said yesterday that VuelaMex has to meet all the requirements in order to get an operating certificate to fly schedule passenger service. So far they haven't...
The specific problem with VuelaMex's application is that the company doesn't have enough money to guarantee a year of operations and the ministry of transportation does not want to have another TAESA (in which mexican tax payers had to pay for most of the liabilities) hurting other airlines finances!
Link to Reforma newspaper in spanish:
Lineas Aereas Mesoamericanas said they won´t start operations until the airline industry recovers from 9/11.