In a statement on the forums, SWTOR Senior Online Community Manager Stephen Reid posted the following:
Due to the design constraints of a fully voiced MMO of this scale and size, many choices had to be made as to the launch and post-launch feature set. Same gender romances with companion characters in Star Wars: The Old Republic will be a post-launch feature. Because The Old Republic is an MMO, the game will live on through content expansions which allow us to include content and features that could not be included at launch, including the addition of more companion characters who will have additional romance options. (Emphasis ours.)This plan is certainly in line with other BioWare titles while setting it apart from other MMOs. Hopefully this option won't end up in the "never got around to it" bin like housing in a certain other MMO.