Is it me or is Dorian a whiner when it comes to his realtionship with his father? That story doesn't make a lick of sense. We are told from DA:O on in codex entries and the like, that sexuality doesn't really matter in Thedas, that it is just a quirk and as long as you perform your duties expected of you, noone cares.
So Dorian's father shouldn't really give a damn that his son is hooked on man-parts, all he cares is that Dorian father him some grandchildren. Now obviously nobody likes being forced to marry against their will, but this is totally accepted in these times. Nobles are married and bred for the sole purpose of forging alliances and getting more wealth/power. It wasn't even uncommon for these marriges to never even consummate and both parties kept concubines.
Add to this that I spent the latter half of the game shamelessly frilting with Dorian, making his "big reveal" all the more anticlimactic.
Not that I don't enjoy his character and romance tremendously, but the whole gay issue seems forced when according to the setting it's no big deal.
As far as I recall, the World of Thedas book establishes that the Imperium is somewhat less "progressive" in public regarding this - which doesn't stop it in the private sphere, though. Going by what I read of this, as I do not have it.
That aside, I suppose it would still be a concern for such families where it is expected of an heir that they do sire/birth the next generation, to secure the family's lineage. After all, Thedas does not have alternate means of procreation other than the natural method, and if an heir's stance is at odds with this, there may be a problem.
I'll have to agree that him swinging the other way was just slightly overplayed in that 're-union' with his father, for the reason you give. Way I personally see it, he could simply have agreed to a marriage for appearances, come to an agreement with a potential wife beforehand - libertine freedom of choice for a lover for her as well as him, say - and done he is.
Even so, I am glad one can talk him into making up with his da', rather than said da' being completely caricatured as the big bad. By and large,it still is family business, and reconciliation in those matters usually works best.
Having said all this, I've got to say I can feel for those who would have loved to hook their Inquisitor-ladies up with Dorian, charming fellow that he is. Despite this, the flirts my Inquisitor ma'am can still throw at him are delightful, this coming from someone who usually sticks to female PCs and hooks them up with girls.