One issue is that the standard tsearch2 install does parsing of the text in the database. So, to index items that are stored in the filesystem the text content to be indexed needs to be stored in the database. Because the installation process would be much simpler than compiling the nsfts.so driver for the external parser, and because nsfts.so is currently not compatible with tsearch2, I think a way to store indexed content in the database is a good first implementation.
Some installations might find storing duplicate text content for filesystem items in the database to be a problem, in that case, an different tsearch2 compatible driver with an external parser can be built.
I have discussed these ideas with Paul Doerwald and Dirk Gomez. Anyone else who is interested in improving the search capabilities for OpenACS, for PostgreSQL or Oracle, let us know by replying to this thread. If you just have a comment or idea, post it here.
More to come.