Although architecture instability has been studied and measured using a variety of metrics, a deeper analysis of which project parts are less stable and how such instability varies over time is still needed. While having more information on architecture instability is, in general, useful for any software development project, it is especially important in Open Source Software (OSS) projects where the supervision of the development process is more difficult to achieve. In particular, we are interested when OSS projects grow from a small controlled environment (i.e., the cathedral phase) to a community-driven project (i.e., the bazaar phase). In such a transition, the project often explodes in terms of software size and number of contributing developers. Hence, the complexity of the newly added features, and the frequency of the commits and files modified may cause significant variations of the instability of the structure of the classes and packages. Consequently, in this registered report we suggest ways to analyze the instability in OSS projects, especially during that sensitive phase where they become community-driven. We intend to suggest ways to predict the evolution of the instability in several OSS projects. Our preliminary results show that it seems possible to provide meaningful estimations that can be useful for OSS teams before a project grows in excess.