1) MongoDB can be used as a data store for security data by scaling out the mongod nodes. This allows for isolation, retention of large amounts of data, and access to the distributed database in the cloud.
2) The document discusses using MongoDB for storing security data and addresses three key challenges - isolation, retention of large amounts of data, and accessing the distributed database in the cloud.
3) A tool called MongoR is proposed that optimizes MongoDB for write-intensive and scale-out workloads through automated data segmentation into buckets, a generator to move data between buckets, and a destructor to remove old data, improving data retention.