With an eye on the current divorce rate, it seems that there are many marriages that cannot succeed, with a man being unable to manage with one woman. How on G-d’s earth does anyone expect hmi to manage with two?
One downside of polygamy is that a man can end up with two mothers-in-law. Imagine! Two shviggers! That is a nightmare!
On the serious side, there is a relatively unknown (it should stay that way) movement to reinstitute the subject of Pilegesh. The advocates for this base their position on a tshuvah from Rav Yaakov Emdin where he discusses the subject. I do not recall his precise language, but it boils down to הלכה ואין מורין מכן, that the halacha is that this is permitted, but one cannot implement this halacha. Pilegesh would not be a technical violation of the Cherem D’Rabbenu Gershom. But it would be highly problematic for a wide variety of reasons.