It's a bit like worrying about someone stealing your car after a catastrophic accident has already totaled it.
“The idea of “Wall St” taking your account (per the title of this article) would have to be the result of such a catastrophic and unprecedented cascade of failures–regulatory, legal, political, and financial simultaneously–that it probably means that your stocks would have lost most of their value anyway.”
Not exactly.
If the brokerage house gets hit with a high level of margin calls, say from crypto or other hedged assets which they cannot cover they need to access other assets to cover -fast. They could claim your assets as their’s to cover their liabilities.
I remember this from the 09 GFC. People on message boards giving advice how to acquire the stock certificates of their shares to prevent them from being loaned out (shorted) by brokerages or used as collateral by the brokerages.