Since we are no longer bringing up little boys to be husbands, and given the extended time-frame of human reproduction, there now is, and will be for the foreseeable future, an excess of women who desire to be wives in relation to the supply of men who can function as husbands.
Under these circumstances, and with the state of the law as announced in Lawrence and Goodridge, legalized polygamy is inevitable, and will come sooner than you think.