how far the liberals push this
As far as they can in other words “were screwed”
From a legal standpoint, the federal courts have been overturning state definitions of marriage. This means that legally speaking, they are setting legal precedents that the states have no right or legal authority to define marriage.
So with that legal reasoning established, it seems to me just a matter of time until we have legal polygamy, cousin marriage, brother/sister, and groups of people claiming marriage rights.
This is an important point. If the courts are ruling that states cannot define marriage, then there is no definition of marriage. Which means that polygamy, triads, group marriage will eventually be legally recognized.