Regarding segments based approach like lucene, means we will need to do segments merging which in my experience quite resource intensive. I don't actually know how blevesearch handles this prior segment based approach.
Merging is required and is indeed somewhat resource intensive. Bleve's current indexing approach has no segments, instead all index data is serialized into a key/value store. This approach allowed us to experiment and plug-in a variety of implementations. Unfortunately, the key/value abstraction limits the way you interact with data, so there are a number of drawbacks. One key gain we get from the segmented approach vs the key/value store approach is that we no longer need to maintain a backindex to handle updates/deletes.
Not yet looking into scorch. So scorch would replace other storage engine like rocksdb and leveldb?
Still very much a work in progress but the core is functional.