I don't remember that many bi-sexual characters. Only two I can think of are Zevran and Lelianna, which it made sense. I certainly didn't find a huge populatiion being bi.
For instance:
I've had to look up online to see what companions I get due to my badluck of choosing female character's whose first companions are also female (except for Khem, who isn't romancable anyway). I also made a male character and wouldn't you know it, his first companion is a guy too Terrible bloody luck there, but oh well. I was thinking of making my second republic character a trooper but this time I checked up the companions online to find that the first companion is also a guy.
however arguments about the gender thing being said, I do see what the developer's vids said about feeling for the characters, which is something that I felt strongly in DA and ME where I actually cared for the characters and wanted to bring them on every mission. I think the same-sex thing should only fit the character, not because we want it to fit which might cause a problem as looking at the list some classes only have 2 romancable characters (1 male and 1 female) so it'll be a challenge. Perhaps we'll get same-sex relationships at the same time they bring us more companions either those companions being same sex or some pre-existing ones being bi or same-sex.