This work is done as part of the Tacos project1 whose aims is to define a component-based approach to specify trustworthy systems from the requirements phase to the specification phase, in the Cycab transportation domain. This paper mainly deals with the improvement of requirements elicitation in the context of Cycab domain. For that purpose, we propose to extend the Kaos goal oriented metamodel in order to enable explicit representation of variability at the early-phase of requirements engineering. This extension allows specifying a requirements family model which integrates both reusable assets and a variability model. The latter expresses the relevant domain facets along with different variants to realize them. The facets allow to structure and organize domain knowledge for reusability. The variability model then enables designers to explicitly state strategic decisions for requirements model development and then choose more accurately the relevant options of the system to-be.