It would be really awesome if someone could actually run the historical test of this strategy, I'm interested to know whether it would help and by how much.
But one thing that I haven't seen considered: I read the Fidelity terms for margin loans and it clearly states that not only can the interest change by whatever Fidelity feels like at any time, but the margin requirements may as well. So it seems entirely plausible that when the market drops and stuff starts looking sketchy, the brokerage gets cold feet and suddenly increases the margin requirements.
Fundamentally, you're putting your financial fate in the hands of a single other entity (or maybe two or three, if you diversify your loans.) That fact alone is enough for me to not want to touch it with a ten foot pole.
I'm not following why you think "the brokerage gets cold feet". Part of their business is making margin loans - they're going to get cold feet about their business? If they're worried they can sell your assets to pay down the loan - that's also in the margin agreement. If they suddenly get irrational, they have competitors to take their customers from them.
If Fidelity suddenly began charging 12%, someone with $50k left and $8k of loans could move 1/2 their assets to IBKR, take an $8k loan there, and pay off Fidelity's loan. Then move the rest. No assets sold - just one margin loan paying off the other. And that 12% is charged daily, so if it takes a month to change brokers, they only charged 1% of the loan value ($80 in this example) before you left.
I would also like to see a simulation. Someone could create a spreadsheet, with years 0 to N, and stock market performance each year. But the margin loan would not happen at the start of the crash - only after markets are 20% down. When markets return to that point, the margin loan is paid off with interest. Then compare that to selling assets for living expenses every year.
Tighter margin requirements are actually a legitimate concern that could make this strategy impractical, even if it looks good when backtested. The Federal Reserve Board sets the minimum standard for initial margin, and they used to actively manage margin requirements. Brokers, however, are free to set more stringent (higher) initial and maintenance margin requirements, and they're free to just say one day "we're no longer doing margin loans, so we liquidated your position". There's no law or contract that says they have to continue lending to you or maintain a particular maintenance margin.
So if IB or Fidelity or TDA or Scwab or Vanguard finds themselves taking on more risk than they can manage, they'll raise the initial/maintenance requirement. For IB, this occurred as recently as September 2020
simply because they could foresee a period of higher volatility around an election that had not happened yet!
https://www.yahoo.com/now/top-brokerage-tightens-margin-trading-as-competitors-stay-steady-144034004.htmlThen there is Robinhood, which just escaped any liability for cutting off leverage to the WSB crowd when they were taking on too much GME risk.
The brokers are paying a tricky game of chasing a tiny margin on a high-risk business. If market prices fall overnight below maintenance requirements, they could be on the hook for losses or out of compliance. So they reel in the risk at exactly the time you'd like to make a low-interest loan against stock collateral.
Strangely, it is difficult to find information about broker behavior during crises such as 2020, 2008, 2000, 1987, etc. My Google only found academic articles with general mentions of the phenomenon. You can bet a table of brokerages during those crises would show them all tightening margin reqs.
Of course, this is also an issue for ERN's non-algorithmic approach of starting out with margin debt. If anything, it means you'd be called sooner, and the outcomes would be even worse.
A HELOC could be used in place of a margin loan IF (a) interest rates on such loans were low enough that it made sense, AND (b) banks weren't shutting down all lending like in 1929 or 2008, AND (c) the value of your home equity has not fallen too far during the crisis.