@dmlc/xgboost-committer Please add your items here by editing this post. Let's ensure that

• Each item has to be associated with a ticket
• Major design/refactoring are associated with a RFC before committing the code
• Blocking issue must be marked as blocking
• Breaking change must be marked as breaking

For other contributors who have no permission to edit the post, please comment here about what you think should be in 1.2.0.

• GPU port of Accelerated Failure Time objective for survival analysis (GPU implementation of AFT survival objective and metric #5714)
• Optimized JSON IO (Implement fast numeric printing routines. #5772).
• Callback function for device DMatrix (Use DMatrix Proxy for implementing data callback. #5629).
• Device DMatrix for dask interface ([FEA][Python] Multi-GPU training with DeviceQuantileDMatrix  #5583, Dask device dmatrix #5901).
• Integrate dask interface with Python asyncio. (dask async operation with XGBoost failed (with Rapids on GPU) #5639, [BLOCKING] [Dask] Asyncio support. #5862)
• Upgrade rabit. (Update rabit. #5680)

Blocking pull requests

• [BLOCKING] Remove to_string. #5934
• [BLOCKING] Handle empty rows in data iterators correctly #5929
• [BLOCKING] [jvm-packages] add gpu_hist and enable gpu scheduling #5171
• [BLOCKING] Thread-safe prediction by making the prediction cache thread-local. #5853
• [BLOCKING] [R] Add a compatibility layer to load Booster object from an old RDS file #5940
• [BLOCKING] [Dask] Asyncio support. #5862
• [Breaking] Fix custom metric for multi output. #5954

Breaking change:

• From now on R and Python custom evaluation metric will receive raw prediction. [Breaking] Fix custom metric for multi output. #5954