According to the PlayStation Blog, the Ship Editor allows for more than just palette-swapping paint jobs – pilots will be able to create their dream human-saving craft, down to the positioning of weaponry, afterburners and setting "attributes to govern the ship's agility, boost and overdrive, and choose either of the standard weapon sets." Non-creative types can just wait for the Resogun community to build the inevitable Nyan Cat-shaped vehicle and download it for themselves, thanks to support for sharing builds online.
If the addition of local co-op isn't enough of a reason to play with new (or downloaded) creations, the free update will add a few new trophies to chase. You can always burn time climbing your way back up the leaderboards, too – the related post notes that due to players finding exploits, the update will reset leaderboards in addition to patching a few of those up.
As great as free content is, the Heroes expansion for Resogun is still launching on June 24, offering Survival and Demolition modes for $5.