Make it a Roth 401k so when unusual things like housing collapse you can pull your principal back out to make a purchase without penalty. Assuming the stock market didn't crash simultaneously.

That is the rule with a Roth IRA - pull out up to your contribution value without penalty. Early withdrawals from a Roth 401(k) are different: if your account is 80% contributions and 20% earnings, any early withdrawal you make will be prorated to be 80% contributions and 20% earnings. The earnings chunk will be added to your gross income and subject to a 10% penalty (in this case, 2% of the overall withdrawal).

Given that most people here are high-ish earners, I’d say a traditional 401(k) is still the most appropriate choice because of the tax arbitrage. If you need to tap it, a 401(k) loan is an imperfect but probably decent enough choice.

I'd say either way, keep your retirement savings and home buying savings separate. Sure, it will be nice to own a home when you're retired. But you're still on the hook for property taxes, repairs, and food.