As many have pointed out, there is nothing magical about nine as the number of Supreme Court justices:

The U.S. Constitution established the Supreme Court but left it to Congress to decide how many justices should make up the court. The Judiciary Act of 1789 set the number at six: a chief justice and five associate justices. In 1807, Congress increased the number of justices to seven; in 1837, the number was bumped up to nine; and in 1863, it rose to 10. In 1866, Congress passed the Judicial Circuits Act, which shrank the number of justices back down to seven and prevented President Andrew Johnson from appointing anyone new to the court. Three years later, in 1869, Congress raised the number of justices to nine, where it has stood ever since.

Franklin Delano Roosevelt’s scheme in 1937 to pack the court and raise the number to 15 did not fly.

Two conservative legal scholars have suggested leaving the number at eight for now, citing many instances in which the court functioned for months with an even number:

Even in the rare cases when eight justices split evenly, 25 times the court affirmed the lower-court judgment without opinion (or precedential value) and 54 times the court set the case for reargument. The former approach allowed the issues to be raised again in similar future cases. The latter allowed for proper resolutions once the ninth justice joined—and only 25 of those cases ended up 5-4, meaning the new justice made no difference in over half of the reargued cases.
In other words, rather than making the judicial system grind to a halt, a Supreme Court vacancy merely delays rulings in a small number of cases. A study of the past 60 years of eight-justice rosters reveals that today’s Roberts court can easily handle the current vacancy, however long it lasts. … Last term only 19 of the 74 decided cases went 5-4. Of those, Justice Scalia was in the majority only six times. Yet regardless of what happens in any particular case, Justice Scalia’s absence—while a huge loss for the nation—hardly hampers the functioning of the Supreme Court even if his seat remains vacant until after the election.

Given all that, here is a plan: Leave the seat unfilled until the election. During the lame-duck session, when 2017 control of the White House and Senate is known, the president’s appointee, as long as qualified, gets his up-or-down vote. The president is insisting on an up-or-down vote but has no recourse now or in December if the nominee does not get the votes.

However, in exchange, if the nominee is rejected, both sides agree there will be no more Supreme Court filibusters. If the next president is a Democrat, she can be assured of an up-or-down vote on her nominee, allowing for a middle-of-the-road justice to be put on the bench if the Senate has a Republican majority and a more liberal one if it is in Democratic hands. If the next president is a Republican, he gets his dream pick with a GOP-held Senate but would need to find a moderate if the Senate is in Democratic hands.

Truth be told, President Obama cannot in his term get his dream pick, or even a middle-of-the-roader, on the court because a GOP Senate wants to find a suitable Scalia replacement. Republicans are content to vote up or down on a nominee, so long as they do not get penalized for it in the election. Both sides have the prospect of winning the White House and the Senate and so have equal chance to get a dream pick, but also are compelled to compromise if the Senate is in the other party’s hands.

Alternatively, the sides can do nothing since the power to confirm or even consider the issue is solely in the Senate’s hands, and it does not seem to be an issue of sufficient magnitude to make a difference in the November elections. Adopting our approach gets the Democrats something they do not have now: the prospect of a real liberal on the court next year. The Republicans get something they do not have: the prospect of a justice in the mold of Scalia.