Has there ever been a situation of perfect bilingualism, without falling in diglossia?
In many places around the world there are different languages that coexist: some people speak one, some the other, and many can speak both.
There are as many cases as situations: some of the languages are forbidden, others are official, while others have some good/bad background.
Over time, if a language is official and offers benefits to the speakers, it is difficult for the people speaking the other to keep it over generations, so it becomes a diglossia: one language is used for certain situations, while the other is used on the rest. Normally, one becomes the official and the other one becomes the popular.
However, I wonder: has there ever been, or even now, a situation of perfect bilingualism in a place, where the indicators of both languages remain more or less equal over the decades? This needs to imply that both languages are official and taught in schools, for example.