I feel like there is room for a third option between those two.
1.5: Both wives at the same time with natural physical contact.
Women frequently relate physically in ways that would be unnatural for men. I am sure you have noticed the difference between how two female friends will hang out on a couch and how two male friends will. They will often share a blanket, sit on the other's lap, or put their head on the other's chest while they chat. Women will go into dressing rooms together to try on clothes, hug more often than two men will, do each other's hair, and generally are more physically comfortable together.
Usually this is more common among young women and they progressivly grow further apart as they distance themselves in an independent, monogamous, and feminist society. If an affinity for intragender physically relating is a female attribute, then masculanizing women will reduce this attribute.
Observing this "natural law" in the differences between men and women is part of what convinced me that polygyny is natural. If a man tries to imagine what would be going through a woman's head when she is touched by another woman, by comparing it to what would go through his head if a man tried to relate to him in that same way then of course he will be affronted! Men are different than women, so that's a wrong comparison to make.
Physical contact between women is, in my opinion, a pretty normal thing. I wouldn't want a massage from a man, and my wife would only want a massage from a woman or from me. Its a pretty stark difference when you think about it. Women are just created to be more comfortable with each other. (That's a clue)
In a plural marriage, I always figured sharing a bed on occasion is something that would naturally occur - like if everyone wanted to be together. If you flirt with two wives all day, you are not going to lock one out at night. If they both want to celebrate your birthday, why stop them? Would you really book seperate rooms on a vacation? You wouldn't take turns changing clothes in a hotel bathroom would you? Sometimes its best to let things take their natural course and not force something one way or another. It probably depends on the personalities of your women a lot too. I'm sure it is probably harder to share a man when you are older and have never done so before.
I get a sense from Scripture that community in worship is preffered over isolation in worship. If we are united by one Lord, then our focus is on him. It doesn't mean that we can't fulfill needs within the body, just that we shouldn't be so consumed by getting a churchy social club high that we ignore the reason we gather.
"Is not the cup of blessing which we bless a sharing in the blood of Christ? Is not the bread which we break a sharing in the body of Christ? Since there is one bread, we who are many are one body; for we all partake of the one bread."
1 Corinthians 10:16-17 NASB
I think that's the line we should be drawing here. Are the women united by the man's body, or by each other's?
"We love because He first loved us"!
(There's a lot in that little verse)
