A great writeup! A lot of startups face the situation that you need to do significant architectural changes to pay the technical debt and re-enable development speed, or improve the performance and scalability of the service. At the same time, stopping feature development altogether for months is impossible.

Incremental rewrite is often the only way to go. I liked how you approached the rewrite with adapters. I'd be very interested if somebody would collect these kind of "rewrite war stories" to a book form and maybe synthesize common patterns from the stories.