Would be nice if mostly only married men and women would live together in the same house and make babies. And maybe most of their free time they would spend together.
Also would be interesting if some men, for example leaders or rich ones, would have many wives - two, three, ten... and maybe they would have concubines as well. To my knowledge, that would be quite historically accurate.
The thing why polygamous marrige could be implemented is this: for example you had a big fight and many men died. Now there is many women with out husbands - widows. Would be interesting if survived men (some of them already have wives) would marrie those widows to increase population growth.