It would be nice to have ModeShape support an excerpt in the result of an FTS query.
That's a feature which is available in Jackrabbit, based on a modular architecture with various {{ExcerptProvider}}s: https://wiki.apache.org/jackrabbit/ExcerptProvider

I suppose that a requirement is that it has to work with all FTS-supporting index providers (i.e. Lucene & ElasticSearch at moment), right?

I'm ready to have a try at implementing such a feature, but I'd welcome some help on where to start and how to plug into the architecture of ModeShape.