The most important contribution that most people make to the economy, labor, is about to become marginalized and become nearly worthless. And capital is correspondingly becoming more important as investment in AI and automation replaces that outmoded labor.
The problem with his reasoning is that only a very small and rich capitalist class will be making those investments. The vast majority of people who used to work for a living will be left out of the economy, with no useful role to play. If they have no money, then, obviously, they will not be making any investments. They'll be struggling to put food on their tables.