Yea, imagine what they'd do during a sovereign debt crisis/dollar milkshake endgame for most of the world's fiats, some fiats are about to roll over because they can't service their debt and yet a few others are spiking because so much debt is denominated in it...

Do they dump all their dying foreign reserves for dollars / francs / gold?

Gold is limited by physical delivery, unless you want to risk it being in a foreign vault subject to confiscation / fractional reserve during the coming crisis...

And with the US is turning off the spigot of offshore dollars, in favor of stables, do you buy dollar-stables and outsource your entire banking apparatus to some foreign company that can simply disable your coins?

Do you hoard oil / iron? China's trying this, but storage is expensive and can only be done with the permission of the US Navy.

Or do you dump those toxic foreign reserves for Bitcoin that you can use to access stables only as needed to service your debt?

The "suddenly" part of the speculative attack won't come from plebs that could always act sovereignly for lack of institutional encumbrance, but from sovereign states once they realize they're out of options.