how do you withdraw without massive penalties if you haven't met the age requirements?
I'm using your post as a jumping off point for a philosophical tangent, so unless you're already a hardcore dedicated Mustachian, read Nothlit's response again and ignore mine.
I think it's great that most people consider the early-withdrawal penalty to be "massive" and look for (and have found) ways around it. That means they truly consider their tax-deferred savings to be "locked up" and untouchable for non-retirement purposes.
But really, "10%" (the amount of the penalty) is rarely a number that's considered "massive". If you're a prototypical Mustachian (high income, short career, low expenses), your effective tax rate in retirement, even with the 10% penalty, is still likely to be well below the marginal rate during your working career. Example: for a couple with $25k/year expenses, withdrawing ~$28,750 from their tax-sheltered account will leave them with ~$25k after income tax and 10% penalty. That's a 13% effective tax rate.
I guess my point is that even in the extremely unlikely event the IRS was to cut off the 72(t) or Roth pipeline methods, it wouldn't be catastrophic for most Mustachians. It would mean adding another year of work to a 15-year career, or reducing expenses 10% in retirement. And it would still remain advantageous to use tax-deferred vehicles vs. taxable; the advantage just wouldn't be as large as it is currently. So even if 72(t) or the Roth pipeline didn't exist right now, I think we would still be advising most Mustachians to use tax-deferred vehicles.