The only problem with that assumption is that holding fiat cash is still basically the same thing as holding sovereign debt when they can monetize or devalue the debt at any time. There is no point in holding cash of a nation with a parabolic debt chart because it's obviously not a safety net. Nobody wants Venezuelan money just because they raise interest rates.
Another thing is that as the USD index increases, most of the world's debt is denominated in USD, so countries who were already insolvent and unable to pay default even faster, causing cascading deflationary collapse to bring down the whole system. Rising USD index is a systemic risk and there is no scenario in which the USD just magically becomes twice as strong, thus doubling everyone's debts and doubling the amount of goods they have to send to America, without everyone completely boycotting the dollar. USD index is already up huge since 2014. The only question is how high can it go before it blows up the system.
The voting mechanism of bitcoin is supposed to be where a Nash equilibrium exists so nobody can collude on any change, so the only changes that can go through are non-zero sum game win/win changes for all. I would say neither segwit or a block size increase actually fits that description in whole, so if bitcoin was actually functioning as designed, it would likely not morph into either one. Bitcoin is supposed to be highly resistant to change and both of them have their drawbacks, so how would either go through?
On the other hand, I don't believe bitcoin has value as a settlement layer because metals act as a far superior store of value and you'd need to get TPS up to something like 5000 where it's not a settlemenet layer to justfiy it's existence.