Speech source separation has gone a long way, thanks to Yi Luo amazing work. With Dual Path RNN, he now achieves almost 20 Signal to Noise Ratio for 2 speaker separation, see [1].
This is a bit of an artificial setting though, only two speakers and they are manually mixed together. I'm not sure if there is any good dataset of speech source separation in real environments (an airport, restaurant etc).
[1]: https://arxiv.org/pdf/1910.06379.pdf
