Heck, Angular is still excellent for large apps as well, as long as there is discipline in your development technique. The issue arises when you have a large team with varying skill levels, all working on the same front-end, with things stuck in the $scope when they shouldn't be, over-use and abuse of $watch, and a stack of other gotchas that make debugging an absolute nightmare, as tracing the execution flow is nigh on impossible.
That's where Flux is trying to do things differently. By having one way of passing data between the various components (and plugged directly into React, which also is built around a "componentized" architecture) you know exactly where to look when things go wrong, you give up a bit of dynamism and magic for explicitness, which in my experience is not a bad thing. That's my two cents anyway!
Really enjoying the Flux design pattern + declarative nature of React. I've been applying the Flux pattern to other applications (iOS) with great successful. The goal of one-way data flow and a single touch point for application events is a radical tool for complexity reduction.
Are you using a Node or Go frontend?
Edit: forgot to mention go-tigertonic. :)