Yes, every countries can follow El Salvador's footsteps also introducing Bitcoin as legal tender side by side with their local fiat currencies inside their territories. There must be just a desire from regulators regards this matter in first place. And that is already the first big challenge, because most regulators aren't interested in promoting Bitcoin to their local citizens, as it's not interesting for the lobbies, monopolies and oligarchs who run the countries.

A deep change of mindset is demand from individuals in order to make Bitcoin an attractive currency to be adopted as legal tender and used for real by a considerable portion of the citizens from a determined country. It's not an easy task, to say the truth. Lots of personal interests are involved, lack of education and conscience by the masses are another challenges which have to be faced.

Abusive regulations is also an issue when we talk about Bitcoin legal tender, because it's possible governments use this regulation as an excuse to overtax its citizens who make use of the cryptocurrency over their earnings.

There are many challenges ahead as this is still an unknown environment for most people and regulators.