What is stopping it's gradual integration?
It's simple, the acceptance isn't there yet for most countries and that's why they cannot adopt it as a legal tender. I'm not going to ask for more about it. As long as they're allowing their citizens to invest and trade Bitcoin and won't ban it, people have already won with that kind of governance. It's too much to ask IMHO about it as a legal tender but countries that have balls to do that can follow what El Salvador has done. And I think that with Central African Republic, they have altered their decision about adopting Bitcoin as a legal tender.Smaller countries see real opportunities in BTC.
Bigger ones - something they cannot control, but can still be regulated and used for what's already in place 
They can regulate it and still continue to allow their people to keep on being involved in Bitcoin. There is no need for them to have that negative thought about Bitcoin unless, these countries have close minded leaders and they want to isolate their people from knowing the truth about decentralization, its power, and potential.