For starters, it gives the impression that "token" characters are the only way to give people LGBT content. For another, a lot of players are already attached to their current companions. So that would be a double whammy. Finally, it would contradict BW's earlier statements that they've had current companions in mind for this all along.
I don't think so. if new companions are released, some of which are gay only, some of which are straight it will be new content for everyone and extend the number of available options for everyone; not just because of the romance options, but also for the companions themselves. If additionally a few selected existing characters would be made available, every single player character would have effectively more options. If in turn same gender romance options are released it will be new content (if on a smaller scope) for people who are interested in same gender romances only, thus, I believe the exact opposite of what you say is true.
Some people may be attached to one particular character and some of them should
be made available, but that would mean that virtually all would have to be available. I don't see the point of this thread as suggesting any particular character, but giving the options at all in the first place. There is no reason why people would like new characters less than existing ones, and the logical consequence of making every single one option work both ways seems most absurd to me.
Therefore, I think you're wrong. New characters would be a lot better than bluntly adding same gender romance options to all existing characters.