The objective of spatially-aware access control models is to regulate the access to protected objects based on position information. In that last years, increasing attention has been paid to spatially-aware access control models for mobile and pervasive applications. Following the experience of design of the GEO-RBAC model, in this paper we want to look at those models with a critical eye and point out open conceptual and architectural challenges. In this paper, we first discuss architectural issues related to the development of a multi-domain access control system based on GEO-RBAC. Then we present the guidelines of a novel and space-centric modeling framework which aims at overcoming the conceptual limitations of the present model and sim...