The eLISA(NGO) mission, the main candidate for the large mission L3 at ESA (theme “The Gravitational Universe”), is a space based interferometer that will observe gravitational waves sources, opening a new window on the Universe. eLISA is in detailed definition phase for a selection in 2017-18. It is therefore essential to evaluate now the scientific potential in order to adapt the instrument for maximizing the scienitific return.