BismIllah wa as salaamu alaikum wa Rahmat Allah.
When I was single and wanted the stability of marriage, I was told by my closest friend that if it wasn't for the physical aspect, she would let her husband marry me. Several years later, in a conversation with another friend, I said that in the event that she was left widowed or alone with her children, I would hope that my husband would marry her so she could be close to us and taken care of by someone good, insha'Allah. I was told that if the situation was reversed, she could not do the same.
Even though I have had two experiences with polygyny, and neither was meant to continue, I still have the same mindset. Of course, I cannot make my husband take a dear and close friend in need as a wife; it is his decision. Of course, it also depends on his tastes and the situation all around. However, my love for certain sisters - those in whom I can clearly see clean hearts and a sincere struggle - makes me want them to be in good marriages, and have them close to me.
It has come to me that polygyny is an acid test of really loving the best for your sister. When there is some disease in the heart, it takes on a different aspect. However, when the sisters involved are truly good and sincere, it breaks my heart that we can be so selfish and put up such barriers.