Starting with 2.8.2 a new major feature is available - replication for percolate indexes.
The replication is based on Galera library (also used by Percona's mysql fork and MariaDB). We considered it would be better to use a tried and proven existing solution rather than inventing a bicycle and build it from the ground up which would have taken much longer.
Manticore Search 3 brings for the first time a breakage in index compatibility and it cannot load existing indexes created with 2.x. This means the indexes needs to be ready before upgrading searchd to 3.x.