Stats-based rebalancing wasn’t enabled by default in v1.1 because it was still possible to cause too much rebalancing with certain antagonistic workloads. It will work great in many cases, but is defaulted off due to a lack of confidence that it will always work for everyone. If your workload is pretty steady, then it should work well for you.
We won’t be enabling it by default in the upcoming v2.0 release either, because no development time was prioritized for it in this past release cycle.
There’s also the option of turning it on temporarily, to trigger some movement of replicas, then turning it back off once you’re satisfied with the new placements. This would get you the best of both worlds – better balance of load with no risk of unexpected replica rebalancing if/when the load changes.