Seriously, I find it ridiculous that these non-human LIs use gender as the hurdle they're not willing to cross - something about Shepard's personality is attractive to them regardless, since Shepard's a human, Tali and Garrus both have an entirely different DNA base, and no matter how it works, because both parties are different species, the... "equipment" won't be a match... But apparently, because Shepard is identifying as a particular gender, they won't cross THAT line? It makes no sense to me.
So yes, bring on the alien LIs for either gender PC!
Qurians are practically human in appearance so I think it makes perfect sense that Tali would not be into a female Shepard. The silhouettes of male Qurians makes me think they look like akin to Bothans from Star Wars under their masks, but it has never been confirmed. If the sexual dimorphism was great enough between qurian males and females(which I can't confirm) I could perhaps see your point.
There are people who will not engage in sex knowingly with a transsexual who looks 100% like a woman. It's not crazy to think gender hang ups would exist with humanoids across the board. Although I find neither attractive I'd take Nyreena over Garrus, Linron over Mordin or Eve over Wrex.