I've been developing in Rails for the last 5 years, and am about to build my own products, and am opting for this kind of setup.. though have decided to hop over to Elixir on Phoenix, and will swap out Redux for Mobx. The application is mostly a dashboard (SaaS). Could easily be an MPA, but I want to move into more responsive UX, and wouldn't mind leveraging the portability for when I develop mobile or desktop apps.

It seems majority of these responses against SPAs are, as you said, all based on bad design, not because the architecture itself is fundamentally flawed -- though it is obviously going against the grain by breaking a lot of this functionality in the first place.

Having said that, the fact that browsers are providing native features to support SPAs, while bridging mobile-native features, is a massive sign of things to come. They're not going away, and support will only get better, and they will only become easier to develop.

Anyway, I'd be interested to hear about your custom router! Any particular reason you rolled your own? I was planning to just use react-router, but if there are headaches down the road in terms of managing a hybrid SPA with SSR, I'd appreciate the heads-up.