In the traditional model for wireless mesh networks, a two-tiered architecture classifies nodes into mesh routers or clients. Such an approach, based on strong separation of roles, is interesting when an administrative entity deploys and controls the network. Nevertheless, in spontaneous and self-organized networks, where there is no administrative entity behind the network formation, this model does not hold anymore. In such a scenario the heterogeneity of nodes should be fully exploited in order to increase, as much as possible, network availability and usability. In this article we propose an approach for opportunistic wireless mesh network formation and maintenance that breaks the rigidness of the traditional architecture. We relax the role separation constraint and consider the case of spontaneous network formation relying on the concept of self-organization and collaboration. The main idea is to make the network take advantage of the specific resources and characteristics of the nodes in an opportunistic fashion. In our vision, any node (routers and clients) can perform any network functionality, if they can and if they wish.