Even though none of us like Gary for what he has done for the crypto industry. But we should be realistic and accept the fact that turning bitcoin into a currency is a difficult task and the chances of it happening are almost zero.
For a country like the USA, it's difficult, but in general, it’s not impossible if a country is willing, and El Salvador is living proof of that. However, I don’t think we should take his statement too seriously. Investors in the US are probably fine with Bitcoin’s current status. As long as they can use it and the government acknowledges it, they likely don’t expect it to become a legal currency like the USD.
People seem to have overlooked the detail that El Salvador does not have its own currency and they use USD as their currency, and the reason they took on the challenge of making bitcoin a legal currency was because their economy was on the brink of bankruptcy and was denied assistance by the IMF at the time. But as fuguebtc said: they make bitcoin legal currency but do they actually use it because as far as I know they still use USD domestically.
For other countries, most of them have their own currency and they manage their people through currency, I don't think they will use bitcoin to replace it and make it harder to manage the economy.
We don't need to listen to anyone, let's take ourselves as the most practical example. Who among us wants to use a payment method with transaction fees and unstable speeds? Is anyone here willing to spend an extra $1-2 (transaction fee) per bill? Obviously, that is not practical and does not benefit us. That's why I don't think using bitcoin as a means of payment is a good idea even though that's what satoshi created it for. With the current changes, bitcoin is no longer suitable as a currency, IMO.