Grand plan is to use pgestraier from PostgreSQL to query Estraier index and Search::Estraier to create index. This would allow to combine structured data in RDBMS with semi-structured data in full text index. Additional normalized tables can be created using materialized views in PostgreSQL, and if all goes well, it will be part of WebPAC version 2 which will be universal hybrid (structured/full text) storage.
Update: I had good luck to find already working perl bindings for Hyper Estraier at MATSUNO Tokuhiro blog. Thanks a lot! So, work on Search::Estraier is suspended.