I've never started a database company, so I don't pretend to know the market the way you do. But I track the database market (open source, commercial, and anything in between) more meticulously than probably anybody on the planet.

I've been working on a series of blog posts since October around the subject to databases and their future, and one post was intended to be my thoughts on RethinkDB. The leak of your postmortem that was revealed on Tuesday has made me reconsider releasing it, but your comment above makes feel obligated to share a few thoughts.

1. The database market is NOT closed. In fact, we are in a database boom. Since 2009 (the year RethinkDB was founded), there have been over 100 production grade databases released in the market. These span document stores, Key/Value, time series, MPP, relational, in-memory, and the ever increasing "multi model databases."

2. Since 2009, over $600 MILLION dollars (publicly announced) has been invested in these database companies (RethinkDB represents 12.2M or about 2%). That's aside from money invested in the bigger established databases.

3. Almost all of the companies that have raised funding in this period generate revenue from one of more of the following areas:

a) exclusive hosting (meaning AWS et al. do not offer this product)
b) multi-node/cluster support
c) product enhancements
c) enterprise support

Looking at each of the above revenue paths as executed by RethinkDB:

a) RethinkDB never offered a hosted solution. Compose offered a hosted solution in October of 2014.
b) RethinkDB didn't support true high availability until the 2.1 release in August 2015. It was released as open source and to my knowledge was not monetized.
c/d) I've heard that an enterprise version of RethinkDB was offered near the end. Enterprise Support is, empirically, a bad approach for a venture backed company. I don't know that RethinkDB ever took this avenue seriously. Correct me if I am wrong.

A model that is not popular among RECENT databases but is popular among traditional databases is a standard licensing model (e.g. Oracle, Microsoft SQL Server). Even these are becoming more rare with the advent of A, but never underestimate the licensing market.

Again, this is complete conjecture, but I believe RethinkDB failed for a few reasons:

1) not pursuing one of the above revenue models early enough. This has serious affects on the order of the feature enhancements (for instance, the HA released in 2015 could have been released earlier at a premium or to help facilitate a hosted solution).

2) incorrect priority of enhancements:

2a) general database performance never reached the point it needed to. RethinkDB struggled with both write and read performance well into 2015. There was no clear value add in this area compared to many write or read focused databases released around this time.

2b) lack of (proper) High Availability for too long.

2c) ReQL was not necessary - most developers use ORMs when interacting with SQL. When you venture into analytical queries, we actually seem to make great effort to provide SQL: look at the number of projects or companies that exist to bring SQL to databases and filesystems that don't support it (Hive, Pig, Slam Data, etc).

2d) push notifications. This has not been demonstrated to be a clear market need yet. There are a small handful of companies that promoting development stacks around this, but no database company is doing the same.

2e) lack of focus. What was RethinkDB REALLY good at? It push ReQL and joins at first, but it lacked HA until 2015, struggled with high write or read loads into 2015. It then started to focus on real time notifications. Again, there just aren't many databases focusing on these areas.

My final thought is that RethinkDB didn't raise enough capital. Perhaps this is because of previous points, but without capital, the above can't be corrected. RethinkDB actually raised far less money than basically any other venture backed company in this space during this time.

Again, I've never run a database company so my thoughts are just from an outsider. However, I am the founder of a company that provides database integration products so I monitor this industry like I hawk. I simply don't agree that the database market has been "captured."

I expect to see even bigger growth in databases in the future. I'm happy to share my thoughts about what types of databases are working and where the market needs solutions. Additionally, companies are increasingly relying on third part cloud services for data they previously captured themselves. Anything from payment processes, order fulfillment, traffic analytics etc is now being handled by someone else.