When the capitalist system crashes in Marx, the proletariat takes control of the institutional apparatus.

Something very similar to capitalism takes its place, with the proletariat controlling the levers.

The main critique of capitalism is not that people exploit one in another in order to build wealth, but that capitalism itself relies on an ideology that first reproduces the conditions of production before it reproduces anything. That's exactly what we see in the markets today, especially with such exotic and abstract instruments in the futures market. They endless proliferation of objects meant to simply reproduce the conditions of production without actually producing anything.

Capitalism under a Marxist regime would be a capitalism that attempts to concretize its metaphors and prevent exoticism and abstraction.

I'm not saying this would actually work.

But I am saying that, and I know this for a fact, a lot of the people working for hedge funds on Wall Street have read their Marx, and ALL of writing can be instantly recalled and accessed in any conversation with one of them. It's pervasive. Now, that doesn't make them Marxists, but no doubt Marxist philosophy enables them to enrich themselves when the critique of capital is used to exploit capital's vulnerability.