Thanks in advance.
This is the question that everyone in the bitcoin space has pondered many times over.
Personally, I tend not to have the view that everyone 'must' adopt Bitcoin. Bitcoin has it's use, it's the door through which everyone must pass - if they'd wish to interact with the digital asset market... this alone, suggests that the user base of bitcoin will continue to grow.
To speculate, it wouldn't be far from rational if digital assets morphed to be viewed more as consumer products - in short, consumer products that behave like financial products.
The way music and movies are categorised into "genres" forces producers to tailor their product to match the needs and behavioural patterns of the end consumer. As a result, the products are laser focused and therefore more likely to meet the needs of the end consumer.
I feel that digital assets should be constructed using this same frame of thought.
In the future, we may find ourselves in an ecosystem in which a variety of digital assets and currencies are built to achieve very specific tasks... self driving cars paying each other... consumers paying self driving cars... universal gaming tokens that are convertible into fiat currencies...
in a system like this, speculators and investors will be betting on the fact that people will continue to pay the fares charged by self driving taxi cabs.... since this activity forces consumers to be frequent purchasers of whichever digital token self driven cars accept, real economic behavior becomes associated with this specific digital asset.
This is more logical than the current status quo in which exchange rates for digital currencies change at random, and with no obvious reason.
and as stated initially, Bitcoin will be the entrance into this market of digital assets.. just like it is today, we must first purchase some bitcoins before we can get our hands on a specific altcoin. Or purchase bitcoins in order to get out of a specific altcoin. This might continue to be the case.
So I don't think every country needs to adopt bitcoin in order for it to be successful. So long as bitcoin ends up becoming the chief currency of the internet, I think growth is somewhat assured