SimC threads have been up on the Trueshot Lodge forums since mid-April. There is a quick-start guide for using SimC yourself, as well as preliminary work on the APL and posts for bug hunting. If you have a stronger APL, bugs to report or want to help get sims ready in general, I'd encourage participation. Class communities are strongest when they collaborate efficiently.
The APL is not in a relatively complete state for any of the three specs yet, and will likely still see iteration improvements well into the raid tiers.
The SimC threads are stickied for each of the three specs. There's now also an initial AMR sim thread for those testing the new sim client.
https://trueshotlodge.ca/forums/index.php?board=8.0