The exact value of all 401k isn't really known, but the average account value is estimated at ~135k, if (let's say) 200 million Americans have a 401k, that comes out to 27 trillion.
In that chart, the 18T of IRA has portion in private equity, and the 15T of pension (defined benefit) has a portion in private equity. The 13T defined contribution plans (of which the vast majority is 401k) can't be placed in private equity right now.
Yeah, but I don't think anybody is expecting every single American to take out 100% of their savings from the stock market and put them in private equity.
It's not, but IRA plus 401k is about equal to GDP, yes (and if you add approximately equivalent defined contribution plans like 403b, tsp, etc, then it's more than GDP)