Looking at the graphs on github you could say development has slowed down, but i'd like to argue that since there is no commercial incentive anymore the project seems to be much more focussed on stability. And when bugfixing you write less lines while spending the same amount of time.
To me focus on stability is the most important thing in a database so this makes me happy as an ops person, get it stable first and then if needed add more features. though i think rethinkdb is already quite feature complete.
In my personal opinion (based on heavily using RethinkDB for two years), many of the core issues of RethinkDB are related to performance, not bugs. I had bet on where RethinkDB would end up performance wise, had development continued with people who really understand how it works doing fulltime development.
To me focus on stability is the most important thing in a database so this makes me happy as an ops person, get it stable first and then if needed add more features. though i think rethinkdb is already quite feature complete.