I read through this thread and found a lot of things that made me want to pop a gasket, but I think the worst thing that can happen to this thread is it being reduced to circular arguments about the same things (esp. in response to things that really require nothing more than air quotes and a facepalm), so I have waited to post until I had a chance to do the appropriate number of facepalms (man, does my forehead hurt

)
That being said, I am a hetero female and neither partial to girl-girl nor to boy-boy romanitc interaction. It's not my thing, yet I
strongly support it being included in a game of ME's nature. Not because *I* want it, but because the game generally tries to allow the player/Shep. as much variety in who they like or love, who they save or kill, basically what they do or don't do as possible. As such, it seems logical that there should also be the option of being in a same-sex relationship; not to "cater to a minority", but to cater to people who play a game that is about a future universe filled with infinite possibilities... ones you want and try to achieve as well as ones you don't want and try to avoid.
As it says on the fist page, the point is to toss around ideas on how to do it. All will have pros and cons, which is fine, but I think it's important to focus on that rather than a generic discussion of whether or not it should be possible at all. The quesition that needs to be discussed is "how" not "if", even if the ideas end up not being implemented in ME, a good idea that has leaked its way through the fanbase to a game developer remains in the developer's repertoire and often finds its way into other games even if it is not implemented in the one being discussed. A discussion which leaves the die hard "no" people and the die hard "yes" people righ where they started holds no value to the developers, nor does it help get anything implemented (now or later).
To the ideas: I think most of the ideas that I have seen on the 1st page show some merit, though of course none are perfect, but none ever will be since we are discussing an addition/alteration to a game that has already come out, which are always more problematic (outside of fan modding) than additions/alterations to a game that is yet to come out. For this reason, I find it more likely that a gay option would be added to ME3 than to ME2, depending on how they want the story to unfold in ME3, of course. While I would still consider it an oversight not to have included the option in ME2, I would support adding it into ME3, at least, if they cannot find a way that suited their overal gameplan for adding it to ME2.
DLC: This has a lot of merit or may even be in planning already given that they say they plan to do a lot of DLC. New characters almost *have* to be introduced in the course of these "expansions" (I doubt the DLC will consist only of "go loot that planet over there" type missions). Introducing a gay romanceable char. in the span of one of the new missions should not be a particular strain on anything, and given as the comic books (from what I've heard since I have not read them) include at least one gay character, it would not be a stretch to have one show up (be it that one or somebody else) in a DLC mission.
BI-DLC: This also has merit, mainly due to the dialogues already being present, but also more complications: an optional download would mean people who cannot pretend that the char. is not bi if they know there is a bi option could leave their game unchanged, but the import for ME3 might become more complicated with 2 different game versions out there (then again this may be simple to solve, I am not programer). Still, I often wonder why the solution to same sex romance always has to be "bi"... Why shouldn't there be a character who is only available for same-sex romance just as there are a whole bunch only available for hetero romance? Nonetheless, if a pure same-sex romanceable character is not planned or requires too much in terms of developement resources, the bi options would work as people can simply pretend in their own playthrough that the char. is hetero/gay/lesbian/bi as they choose.
Either of the above + Color-coded flirt choices: I am torn on this one... I hated how I had to yell at Liara and Kaiden in ME1 to get them to back off even though I was not intending to romance either of them (I simply could not find a way to have a friendly convo with them without getting a flirt). In ME2, however, I found the flirt options very clear and avoided them, no problem (i.e. don't ask if he's single

). If the options are clear in the text, I don't think they need color-coding (no one's fault but your own if you don't read what you're clicking on, imo). If they're not very clear-cut, then color-coding could be a big help for everyone trying to avoid unwanted romances f/m or f/f or m/m. I do share the concerns on breaking immersion, but charm/intimidate choices are already color-coded, and all it really does is make me go "yay, my paragon points are helping me!", so perhaps it wouldn't matter.
Personally, I favor the new char. DLC, but I would have no issue whatsoever with putting the existing Thane/Tali dialogue back in. Which of these is the more doable is a decision a dev/programmer would have to make.
If neither of them fit with their overall gameplan, I would, at least, encourage Bioware to put in a male same-sex option for ME3 (heck, they're probably going to need to put in a few new chars. anyway for certain eventuality-type reasons that would be spoilers, so I'm not elaborating

).
I think it's great that so many people bring up ideas (on diverse topics and levels of gameplay) for improvements on these forums. Certainly, not all will be implemented, but you can never have too many ideas for a creative process of this kind. I have several friends in the game developement business, and they all say that they love to hear from people who have constructive ideas for improvements of whatever kind.
Keep it going, keep it positive, keep it full off ideas! Saying, "Your game was great, but this is something that could make it even better" is the best thing a player/fan can do to improve the franchise (not just for a current game, but in general).
I support same-sex romance option(s) for ME!
Good night and good luck