Do you think that Johnson's statement (from 1921--the year the preface was written) has been realized today?
Johnson's statement: "The richest contribution the negro poet can make to the American literature of the future will be the fusion into it of it's own individual artistic gifts." From the preface to The Book of the American Negro.
The answer to this question highly depends upon one's own beliefs regarding the importance of African Americans' contributions to American literature. On some sides, one may believe that African Americans have made a rich contribution to American literature. Others, unfortunately, will continue to disregard African Americans' contribution to literature in America based upon the following:
Some groups in the United States and Canada do not value multiculturalism: Their ideologies promote the alternative of one unified culture as the only means toward empowerment.
The one literary ideology which would acknowledge the contributions of African American writers is Multiculturalism. Multiculturalism is a "movement" which supports
appreciation, acceptance or promotion of multiple ethnic cultures, applied to the demographic make-up of a specific place, usually at the organizational level, e.g. schools, businesses, neighborhoods, cities or nations. In this context, multiculturalists advocate extending equitable status to distinct ethnic and religious groups without promoting any specific ethnic, religious, and/or cultural community values as central.
Based upon this, one could justify that the majority of America accepts the rich contributions of the African American community. Therefore, one could, comfortably, state that Johnson's statement has been realized today.