Crucible Labs was shipped with yesterday's update and the first time we get to see it is today when it becomes available in a separate playlist.
They said on Bungie yesterday:
As noted in our most recent Roadmap, Crucible Labs shipped with Destiny Update 1.2.1. While the content has been downloaded and installed on your platform, the feature is not yet available. PvP Design Lead Derek Carroll has some information to set proper expectations for the feature, and what to expect when it becomes available:
After this, it was queried on Twitter to see if this extends to Sandbox changes. Here's the answer:
Josh Harnick added to this to explain it would be difficult to bring a different sandbox to a live environment.
I'm pretty disappointed tbh. They released this info on the day it was available so that tells me they knew it wouldn't go down well. It will still be fun if we get to play some truly different game modes but I hope its not just a control game with slightly tweaked spawns or subtle score changes.
I can now see why they called it Crucible Labs rather than Destiny PTR, so more fool me to assume it meant that (as too the thousands that thought the same).