Reason for bumping the default:
Denser DataNodes are common. It is not uncommon to find a DataNode with > 7 million blocks these days.
With such a high number of blocks, the block report message can exceed the 64mb limit (defined by ipc.maximum.data.length). The block reports are rejected, causing missing blocks in HDFS. We had to double this configuration value in order to work around the issue.
We are seeing an increasing number of these cases. I think it's time to revisit some of these default values as the hardware evolves.