- lack of mass adoption - they didnt solve a problem everyone had
- lack of nitch adoption - they didnt solve a problem a few people had badly
I can tell you 4 features that I view more important than change subscription
- can run in any ecosystem - pouchdb/couchdb and waterline are examples of single apis in different environments. Even being able to use the database 100% in memory as a redis alternative would be nice.
- supports transactions across shards natively - this is a difficult but important feature that mongodb is missing
- supports document id transaction and table transaction - if Im only updating two documents, I have no interest in making many financial transactions wait for a table to be finished being used when I only care about 2 documents in that table.
- "sync" feature on a table - pouchdb supports this for syncing a client with a server
Rethinksb failed because, despite its sweet name, it wasnt solving that important of problems.