When? I think you are writing this as a warning to people going down this path, but I wanted to point out that they ran into this stuff once they reached a certain size. That threshold may be quite high. Does it happen at 200 engineers? Or 1000? Or 100? At any of those sizes having some people do this work doesn’t seem like that big a deal.
Relative to what? I got to watch some companies go through the “grow from 50 to 200 employees” transition, the amount of time and energy spent on getting microservices and multi-repos working was really high. There was a dedicated team and lots of projects had to integrate with that, and the integrations weren’t friendly for all different languages. Point is, a serious amount of work exists on this path as well.
In summary: It seems like companies go from monorepo to multi-repo back to monorepo as they grow, and I’m not convinced that means it is the fastest, cheapest, or easiest path.