The CTO I am working with is responsible for maintaining both MySQL and MongoDB data stores himself in addition to writing a lot of code. After starting with My

The CTO I am working with is responsible for maintaining both MySQL and MongoDB data stores himself in addition to writing a lot of code. After starting with MySQL he has been gradually shifting everything to MongoDB and would like to just get rid of MySQL. I personally don't have deep operations experience, and I am sure your individual experience is valid. I think that in part, MongoDB is maturing- it now has single server durability and replica sets. Single server durability means it now can be a default, whereas before you had to commit to 2 servers as you allude to. People seem to report it is more critical to have enough memory, and that it wants more in comparison that a SQL database, so perhaps that limits its ability to be a default database. The issue of course isn't whether you can adjust an RDMS based infrastructure to suit your needs, but how much effort that will be in comparison to an alternative.