The term 'race' is a social classification. It means that it's a man made term. To designate oneself as being part of a certain race is sometimes an individual choice - not one that is placed upon you necessarily. (Sometimes race is based on the colour of a person's skin - so someone who is black is a social classification that others have placed on them and it isn't necessarily a personal choice.)
In this sense - asking a question like, 'Will everyone be mixed race in the future?' is a bit odd because in the future some will probably consider themselves of multiple races and others will continue to consider themselves of a single race.
In the sense of bloodlines - we're not really of any race at all. We are of different ethnic backgrounds (since they're individual social choices), but not necessarily of different races.
I am technically half south-east Asian and half Caucasian, but to be honest I dislike heritage pride and reject this. I believe that the only race on Earth is the human race, and that race something created by society. Furthermore, the definitions of race classifications have changed through out history, and no doubt will change in the future.