I liked that your post didn't start with "we use MongoDB and there's some problems with it". I haven't used MongoDB on production, and while I'm interested to learn about specific issues, the format of this post gives the reader the opportunity to evaluate your problem from a platform-agnostic perspective first. Instead of having Mongo interfere right away, I can think about how our systems might hit the same issues.

To echo others, I'm interested to read the more in-depth post-mortem.

Good luck!