Caveats.
There has never been polygamy in a country with a technologically advanced economy. The closest was Utah in the 19th century, at for a while Utah led the world in terms of women entering professions and having career. It would be an interesting experiment.
If the “shiduch” crisis is caused by a shortage of frum men (which suggest frum men go off the derekh more than women, or that most Baalei Tseuvah are female – and I doubt that either is true), polygamy would solve the problem. But the problem probably has to do with the economy causing men to be slow to want to start families they can’t support.
Polygamy would not be common, absent a shortage of men, since few men could support multiple housewives. The exceptions would be the superrich (of which there aren’t many), or if something such as a war kills off most men (very rare, especially for Jews).
Any change in law would allow multiple wives and multiple husbands, meaning the government definition of a family would be wildly different than our own. This would be interesting as well.