Smalltalk is a fully reflexive object-oriented programming language created in the early 70's. Over the years, it has been influencing many other programming languages and evolved into many variants. However, it has no notion of visibility, providing a single namespace. Because all classes and global variables were visible from every point of the system, numerous dependencies appeared and it turned into a monolithic system. As a descendant of Smalltalk, Pharo should provide a programming construct to make the platform more modular. Designing such a construct is a challenge because of two migration constraints: it must support circular dependencies and local class extensions. In this context, this article present an analysis of the design space for a module system through three design axis: encapsulation, dependency resolution, and module combination.