Here's an idea I've been running through my head, a potential work-around for how to reform the Supreme Court that won't benefit one party or the other:
Any time a new president is inaugurated, they receive the right to appoint two new justices to the Court, within four years' time (no more than one new appointment within a year of each other). This allows the Court to have a flexible number of justices, and ensures that the new president's agenda gets a seat at the table, judicially-speaking.
There obviously have to be other reforms to how a justice is confirmed, too — this idea wouldn't prevent Republicans, for example, from blocking every potential justice Biden would select "just 'cuz," if this proposal had already been in place. Tenure limits should also be instituted to prevent the Court from getting too large.
But I think this idea has merits in how we can make things less partisan, so that blocking nominees is seen as less "necessary" in some lawmakers' minds, especially if they know they have a chance to win the presidential election and nominate two new justices later on.
"Packing the Court," as some have alleged Biden and Democrats are attempting to do, is seen as blatantly partisan — even if it's somewhat justified, given how Republicans have acted in the past (blocking Merrick Garland but bending over backwards to justify approving Amy Coney Barrett).
This idea allows for a regular "flow" of new justices, but not at a pace that's too quick, and in a way that might appeal to all sides of the political spectrum.