The math still works, especially in light of the insane inflation we're experiencing right now. Hopefully, both will stabilize sooner rather than later.
A long time ago, when I was getting the DPOYM lesson pounded into my head (long before MMM was born), I remember being thrilled to buy a new place and get a 7% mortgage, and I had stellar credit. Mortgages are still historically cheap.
The math still works, it just isn't quite as blindingly obvious.
See, I have this theory that monetary policy is stimulative any time you can borrow for less than the rate of inflation. E.g. Toyota is
still offering 1.9% financing for new cars that will likely cost 6-8% more to buy if you wait 12 months PLUS a much higher financing rate (and you also miss out on the utility of a new car until then). Thus it makes sense to pull forward next year's planned purchase of a new car and lock in the lower price today. Even if you park it in a storage unit for a year, the depreciation won't cost as much as the price and rate hikes!
Similarly, even though mortgage rates are suddenly 6%, it might still be justifiable to buy a house today because the inflation rate is more like 8% and all the labor and commodities that go into building a house are getting more expensive by the day. When you can borrow at a cheaper rate than inflation to lock in lower prices than will be available in the future, you are incentivized to pull ahead your purchases. This logic applies to corporate investments too: Borrow now at 5-6% to lock in next year's supply of inventory or commodities and avoid the next round of 8% or worse price hikes.
This dynamic, of course, leads to higher demand, shortages, and higher inflation expectations, which means the rationale for spending money keeps making sense month after month until the music stops.
With mortgages you have the option to pay them off or refinance when the rate of inflation drops back below your interest rate - i.e. after the next recession. That option value makes RE seem like a win-win to a lot of people.