The development and safe operation of future national- and continental-level power systems calls for an open and flexible modelling environment that allows to easily introduce new models, adapt existing ones, and share them among national Transmission System Operators, as well as to integrate power system models with physical prime mover models. The Modelica language is being considered as a candidate for this purpose. This paper reports the first results of a feasibility study regarding the use of Modelica for large-scale electro-mechanical power system models, with many thousands generators, loads and transmission lines.