I don't think he's arguing that the existing functional languages can't take advantage of all cores, it sounds like he believes that the existing functional languages cannot reach mainstream adoption because of fundamental flaws that he hopes to address:
> My conclusion is that there are major, well-justified reasons for why people strongly dislike functional languages. The hypothesis I aim to test with a new programming language is: By making different tradeoffs, these issues can be mitigated and a more broadly-appealing functional language can be built. With such a language, I hope that the true promise of functional programming for parallel computing can be widely realized.
> My conclusion is that there are major, well-justified reasons for why people strongly dislike functional languages. The hypothesis I aim to test with a new programming language is: By making different tradeoffs, these issues can be mitigated and a more broadly-appealing functional language can be built. With such a language, I hope that the true promise of functional programming for parallel computing can be widely realized.