Instead of an app directory you put all your code into gems and engines.
Shopify has taken the approach of siloing their monolith into smaller rails apps which is a similar approach to refactoring into rails engines.
The microservice architecture seems to mainly function as a way
to impose discipline on programmers who lack self-discipline.
Microservices won't change any of those variables. Nor will it change the normal distribution of them. So one thing is for sure. No matter what the architecture of paradigm is being used, we can on average expect average quality software. Most people on average don't gush about how amazingly clean their architecture is or how well defined their bounded contexts are. They tend to talk about spaghetti. I infer from that that on average it's spaghetti and theres a chance it might not be.