Shifting towards higher penetration of diverse renewable energy sources (RESs) in power systems is motivated mainly by reducing carbon emissions. In the long term of several decades, which we refer to in terms of the future grid (FG), balancing between supply and demand will become more challenging. Also, displacing conventional generators with RESs, especially inverter-based and intermittent RESs, could have significant effects on performance and stability of FGs. So far, FG feasibility studies have mostly considered simple balancing, but largely neglected network related issues such as line overload and stability. The main contribution of this paper is to present a simulation platform for performance and stability assessment of FG scenarios. As a case study, preliminary results on the balancing and stability of the Australian National Electricity Market in 2020 are illustrated with the increased penetration of wind and solar generation in the grid. Simulation results illustrate the importance of power system stability assessment for FG feasibility studies. Keywords—Balancing, electricity market, future grids, power system stability, renewable energy sources