David Friedman at his fascinating Ideas blogsite speculates on the future of families.
Paternity testing means that monogamy is not needed by men to insure that the children they raise are their own. Indeed 'it is now possible to combine any mating pattern from strict monogamy to complete promiscuity with assured paternity'.
A constraint here is that male sexual jealousy may be hardwired by evolution (this link also discusses distinctively female non-sexual jealousy) which will motivate something close to conventional monogamy. A taste for promiscuity however may offset this leading to some form of group marriage. To some extent this has already happened, driven by a slightly older technology—reliable contraception.
Friedman recommends the alt.polyamory web site of interest. This gives access to chat rooms and other online resources.