I like the way someone on Twitter put it: the Dems should filibuster until one of two conditions are met:
A) A rule is established that no President can nominate a SCOTUS pick in the last year of their presidency, which would validate the Republican tactics from last year but officially establish a rule to prevent filling seats in the Supreme Court for a year at a stretch. This would fast track Gorsuch's nomination over Garland.
B) Establish the rule that a President has the full authority to nominate a SCOTUS pick in the last year of their presidency, which would open the doors for Garland's nomination to be heard/potentially confirmed before Gorsuch would be considered. This would prevent the logjam from last year from repeating in the future.
Both options have the effect of restoring legitimacy to the process and preventing political posturing from keeping a seat unfilled for a year on flimsy justifications.