If you’re entertaining visions in your head of player-owned structures or absurd crafting systems, it’s important to note here that “sandbox mode” simply means an option to set up specific practice scenarios. The positive side effect for players at all levels is that you don’t need to wait for a few dozen matches to go just right for you to practice your skill at aiming a skillshot or killing the right targets. It’s a boon for players trying to get better, and while we can’t say it is happening, it’s back on the table for discussion.
Source: Greg Street via Rock Paper Shotgun