It seems odd to me. Paradox is a Swedish company, and Sweden is a fairly liberal country. Same-sex marriage was legalized in 2009, and even the Church of Sweden gave the go-ahead on performing same-sex marriages the same year. The game logic around this is simple enough that changing two byes fixes it, so it's not a technical issue. What gives?
Presumably the AI would have the ability as well, and then you would have to start coding some restrictions to avoid a dynasty simulator spanning 100s of years going off the rails and then you'll be in for all sorts of progressive political wrangling.
Frankly if it was me I'd have stayed well away from it as well.
Also, Paradox have not a great track record of balancing things or maintaining quality straight out of the gate with their games anyway. I do love their games though.