Description
Existing connections are not required to reset their shard versions (via setShardVersion) unless the major version of the shard changes, however new connections are required to have both the same major and minor version of the shard to connect. Checking the minor versions leads to unnecessary config reloads when the highest-version chunk of a shard splits, and makes reloading config information in mongos more complicated and inefficient (requires full reload or an $or query with #shards clauses. For large clusters, this is potentially slow).
Backwards compatibility should not be affected, as this makes mongod more permissive.