When I have prayed about it, the answer that I have always received is that there are a lot of misconceptions surrounding this issue, and that there will be a lot of people who are surprised at what really occurs in the next life. I have had the distinct feeling that plural marriage is definitely NOT a requirement....that those plural families who are eternally sealed, and wish to remain so, will be honored....However, monogamy will be the "norm", and that the definition of celestial marriage is a temple marriage, PERIOD. In other words, as long as you are sealed to your spouse, that entitles you to all of the blessings associated with the CK.
What you say is backed up by Bruce R McConkie.
Plural Marriage is not essential to salvation or exaltation. Nephi and his people were denied the power to have more than one wife and yet they could gain every blessing in eternity that the Lord ever offered to any people. in our day, the Lord summarized by revelation the whole doctrine of exaltation and predicated it upon the marriage of one man to one woman. (D&C 132:1-28.) Thereafter he added the principles relative to plurality of wives with the express stipulation that any such marriages would be valid only if authorized by the president of the Church. (D&C 132:7, 29-66.)