There are several reports and white papers which attempt to precise 5G architectural requirements presenting them from different points of view, including techno-socio-economic impacts and technological constraints. Most of them deal with network slicing aspects as a central point, often strengthening slices with slice isolation. The goal of this paper is to present and examine the isolation capabilities and selected approaches for its realization in network slicing context. As the 5G architecture is still evolving, the specification of isolated slices operation and management brings new requirements that need to be addressed, especially in a context of End-to-End (E2E) security. Thus, an outline of recent trends in slice isolation and a set of challenges are proposed, which (if properly addressed) could be a step to E2E user's security based on slices isolation.