I don't think you're opposed to the idea. You're just worried about development time, fair enough.
But if we dismiss that "potential" problem we're still left with a story that doesn't NEED archetypes, no reason for it. The story doesn't need a complete overhaul due to the gender of the spouses or the child, honestly at most just voice actors and a bit of writing. There isn't a huge (or any?) major difference between same six parenting and opposite six parenting,
So at the end of it I still don't really think there's THAT much work to be done: a few simple rewordings and different pronouns used. Although for a richer world I'd like some acknowledgement/difference.
But yes hiring voice actors and programming and stuff IS work and money, but I don't think it would take more than a week and a handful of people and wouldn't affect the straight part at all. It's a huge team with a huge budget, they shouldn't leave this for the modders, could be kinda condescending considering how much money they'll make from LGBT gamers expecting to "play as whatever character you want".