Thanks for presenting an actual argument. However, I am not persuaded by your argument. First, there is the timing issue noted by the commenter below. Second, in general, speculative bubbles are
not driven by retail savings, or the idea that they are some how extra easy money. Speculative bubbles tend to be driven by (a) sustained periods of market irrationality; and (b) low interest rates. Interest rates are driven primarily by the Federal Reserve, not by retail depositors. The housing bubble in particular was inflated in large part by overly liberal granting of unaffordable mortgages on the expectation that housing prices would continue to grow. Issuing mortgages is a classic commercial bank activity, not an investment activity. The contagion to the wider financial system was through repackaging of mortgages into derivatives, something that was largely done by entities with no commercial banking activity, such as Lehman Brothers, Goldman-Sachs, Fannie Mae, and Freddie Mac. Combining commercial and investment banking under one roof was not particularly involved as a driver of the crisis.
I am also not persuaded by your linked argument as an argument for Glass-Steagall. It argue for the Volcker rule, which is not the same thing as any former provision of Glass-Steagall. I am not sure why the author relates the two, other than perhaps the fact that Glass-Steagall is a popular talking point. To be more clear on the difference, the provision of Glass-Steagall that tends to capture the popular imagination, and which was repealed in 1999, was a rule against combining investment banking and commercial banking within the same entity. The Volcker Rule would instead forbid banks from trading for their own account, while still allowing them to combine commercial and investment activity. I don't have enough knowledge of the Volker rule to argue for or against it, but I the sketchy argument made in its favor and the attempt to conflate it with Glass-Steagall are not terribly persuasive.
Finally I don't think there is any onus on me to offer an argument against Glass-Steagall, until someone presents an argument in its favor. Surely the burden of proof should be on those favoring a new regulation. That being said, the major reason the rule was repealed is that it made US banks uncompetitive compared to foreign banks, with no clear sign that the US banking system was more stable than foreign banking systems as a result. There is no particular reason to think this has changed. So reinstating the rule would make US banks less competitive and perhaps drive more financial activities overseas, for no clear gains.