Most characters are not all too deeply involved in the class story anyway, apart from the way you pick them up. The existing characters were never designed with the intent to use them for more than one class, and yet I don't see a reason why Tharan for example would work for all republic classes. That the class story is different for all classes is therefore irrelevant, even though it will cause design overhead for integrating them, but that's inevitable either way. If you create different characters for every single class, that will cause considerably more overhead and consequently yield less characters becoming available.
They could do it, but my point is still that people won't necessarily be happy with it.
When it comes to sexuality the gender matters a lot. Some people are simple not gay. Of course in some cases we'd like them to be, but the game would be shale if all companions would simply be whatever we want them to be. DA2 is not a particularly good Bioware game - I don't find it bad either, but it's certainly not par with Dragon Age: Origins are the Mass Effect series.
And some people simply won't be attracted to a different species or someone who has different morals form them, but the game in it's current state doesn't reflect this. These things also matter a lot.
I'm not commenting on how good/bad DA2 was...I don't think it matters here.
From what we know now, they won't make all romance companions available to both genders and all I'm saying is that people will be unhappy when it comes time to find out who's available (and not). This is partly the reason I went ahead and leveled my toons in spite of not having SGRA yet...I honestly don't think they'll make any characters available that I'd be interested in anyway so I don't see the point of waiting.