Yeah, I think Sebastian is a romance that is probably more palatable to some asexual players, but he's definitely not (canonically, headcanons are great and all, but canonically) ace.
A relationship with a trans character, imo, is totally seperate from sexuality concerns for me, and I'm not comfortable with the idea of "you guys take him/her, we have less options, we want the cis one"...but that's a whole nother can of worms.
I would love a KISA trans LI though. Either gender. That'd be fabulous.
More of the idea of niche. Since
gay romance is already a niche, so if it's a niche within a niche as opposed to a niche within a broader spectrum which will have more audience.
Trans characters would be very controversial if they did make one a LI, especially if it's one of the options for straight males in which they will complain about the
gay agenda and being shortchanged, even if it's a bonus option. I don't think Bioware will try that, but they could probably add someone like Maevaris as a companion, even if she's not romanceable .