As Segall points out, that's already the case for the vast majority of issues.
But that's not a proper analysis.
Most decisions aren't 5-4 because most decisions are simply more obvious to the Court, regardless of their left-right persuasion.
It's not like most of these cases are 5-4 originally and then one side persuades the other side and it becomes 7-2 or 9-0.
The simple truth is that most cases are uncontroversial for the SCOTUS and the outcomes would likely be the same whether there were 7 conservatives or 7 liberals.
But for the handful of divisive cases, it fucking matters. And there's no evidence 4-4 split would change in these cases.
As an aside, I'd also like to point out that the GOP would put a 5th conservative on the Court the moment they get the chance again because they don't give a fuck about anything else but maintaining their power. The GOP would never play nice so why should the liberals?