[2] The Etsy article from 2012 had the major point "if you are considering Mongo plus another database like MySQL, then in all likelihood you shouldn't do it [...] Keep in mind that almost none of this is specific to MongoDB. I wouldn't discourage anyone from trying Mongo out if they're starting a new site"
[3] As one commentator stated, "don't use a non-relational store when you have relational data."
The most important thing you need to do is probably confirm your feeling regarding a document database being the correct decision for your domain. [2] and [3] concluded by using MySQL rather than MongoDB, but for different reasons. Why do you think a not-MongoDB, but not-SQL database is correct for you?
[1] http://pastebin.com/FD3xe6Jt was debunked in 2011 when it first appeared.
[2] The Etsy article from 2012 had the major point "if you are considering Mongo plus another database like MySQL, then in all likelihood you shouldn't do it [...] Keep in mind that almost none of this is specific to MongoDB. I wouldn't discourage anyone from trying Mongo out if they're starting a new site"
[3] As one commentator stated, "don't use a non-relational store when you have relational data."
The most important thing you need to do is probably confirm your feeling regarding a document database being the correct decision for your domain. [2] and [3] concluded by using MySQL rather than MongoDB, but for different reasons. Why do you think a not-MongoDB, but not-SQL database is correct for you?