It is always tempting to look abroad to Europe for what lies ahead. In the next ten years as Europe becomes more Islamic polygamy will become legal. Already at the furthest reaches of the left in Sweden this is being discussed.
The USA will not likely get to that stage for another 30 years or so.
On a liberty based standpoint those on the left are a tad odd. It is acceptable to limit the size of a beverage and tax fast food but sexual liberty is a given.
Societies adapt and change but life seems best when households are basic couples that want to stay together long term. Larger groups just seem inherently more unstable but that will be for future generations to decide.