Tigase itself is great in clustering, but current supported SQL database like MySql, are single point of failure. I am not sure how Production Ready is Tigase MongoDB implementation, but MongoDB is known to have issue cause single point failure(Master-Slave architecture) and doesn't scale very well.
Cassandra DB seem to scale linearly, no single Master node and many other true cluster features. I see the feature #1058 already in the system, but has been there for two years. I hope Cassandra DB support for Tigase could be implemented soon. This will make Tigase a true Cluster XMPP server