OK, so you don't "tunnel writes through" EventReduce, you "tee" them to EventReduce.
Anyway, to maintain consistency, you have to limit yourself to one process of your app. No sharding, load-balancing etc. This is significant limitation, and it's not obvious. I encourage you to mention it in README.md.
I encourage you to read the readme and check out the demo.
EventReduce is nothing magically drills out your database and affects the consistency of your write-accesses.
It is a simple algorithm that is implemented as a function with two inputs and one output.
Then I fail to understand how it works. How Event-Reduce becomes aware of these "write events"?
>this is an open source project, not something I want to sell you
You made it open source so others can use it, right? They better be making an informed decision whether your solution suits their needs.