This is the problem BioWare had with DAI in that Straight Males looking for Straight Females had very limited choices. Well actually just one ... and she looked and acted like a man. But she had boobs so ...
Anyway I don't suppose I have a problem with everyone being Bi since I'll just play the companions the way I want like I did in Skyrim. My only issues would be if making them bi 1) makes them more generic and, 2) if making them bi means my straight character (or gay) gets hit on by the six they are not interested in. The advancement of the relationship would need to be completely on me WHICH in and of itself makes the characters weaker since being 'hit on' by someone you do like is actually one of the coolest things you can experience in life.