How do you imagine a liberal majority would come about within the next few decades? This was engineered over decades and now the conservatives have all the marbles; that's why they feel so free to rule how they've always wanted.
I imagine you’d need circumstances similar to those that nearly resulted in the Judicial Procedures Reform Bill of 1937, which would have granted Roosevelt the ability to appoint 6 additional Supreme Court Justices. Namely:
- National crisis unifying popular support for liberal legislation.
- Liberal control of the executive and legislative branches.
- A series of supreme court rulings that effectively thwart a popular liberal agenda.
I have no idea if this is likely; however it nearly happened less than a century ago during a period with noticeable parallels to our circumstances today.