I think he would consider it when the economic forces are "fully developed" (which wasn't the case with, say, rail at the time). Of course that itself is a vague term, but once something is a natural monopoly or duopoly the need for capitalist accumulation would diminish. Lenin of course felt a socialist state could develop these forces anyway, with mixed but mostly positive results.

Note that this is exactly how China is working, use capitalists to develop an industry to "mature" status, then merc the billionaire and nationalise the industry. Xi reads theory.