mainstream is exocentric
Exocentric
Different from the regular/mainstream.
Treating or representing someone as different from mainstream behavior
(n. ph.) The culture of most people, the normal way of acting.
The prefix of the word counterculture is counter. In this context the word means against culture or not mainstream culture.
Exocentric
exocentric
endocentric
It is an endocentric compound ;) It's a kind of yard where there are graves
In an endocentric compound, one element is the head that determines the category of the compound, while the other element specifies the meaning more precisely (e.g., 'blackbird,' where 'bird' is the head). In an exocentric compound, the meaning does not rely on one element to determine the category, and the compound's meaning must be derived from outside the compound (e.g., 'pickpocket,' where the compound does not fit strictly into the category of either 'pick' or 'pocket').
Cold water is an endocentric construction, since it functions as would the noun water. Greenhouse is an endocentric compound, since it is a noun as is its head house.
'A new era of media message' is not a complete sentence. But yes, it is an endocentric phrase, because it can serve as a noun.
I am not an expert on this but, yes, I think it can be. Here's why:Anyone is a pronoun.Any is an adjective, determiner, pronoun or adverb.One is a determiner, a number, a person, a thing, a noun, an adjective or it can be used as a pronoun.A further example: The noun bittersweet is an exocentric compound, since it is a noun but its elements are both adjectives. (But, yes, bittersweet can also be used as an adjective!) [Example borrowed from dictionary.com]
mainstream subjects
the mainstream of American culture.
Mainstream EP was created in 1998.
Mainstream Money was created in 2006.