Since when? They are already having custody disputes. How about the two women who just split. The genetic mom (whose eggs were inplanted in the partner) lost the kid. Don't say it's not an issue. It certainly is an issue.
Homosexual mother or father cases are handled in the category of paternity actions. They are not handled directly in the dissolution of marriage area.
Homosexuals use intervention to produce children. The very rare exception of a father or mother who comes out is just a regular divorce case in which you can use the homosexual lifestyle to deny residential custody and in some cases, upon providing expert testimony, obtain supervised visitation with no overnight stays.
There will be no presumption of paternity with two lesbians. Legally it will be as if singly mother married "some guy" not the legal father of the child.
Essentially the ABA Model divorce code which has envisioned imposing homosexual marriage on society, wants to eliminat all children from marriage an place them in the limbo of the dependency courts.