I think making Ruby typed is a cool endeavor. It's just that it's a bit hard to justify from a business perspective..
It's not like changing to typed Ruby wouldn't affect the code bases. They'll end up having something that will resemble Ruby, but likely won't be quite Ruby. It's unlikely they could automate it.
They'll have to rewrite a lot of code and typically, when you do that you also want to refactor obvious problems, so you end up rewriting big parts.
And that's in addition to the cost of trying to make Ruby typed.
Or you could leave the code base as it is and extract functionality out and rewrite it in something more manageable.
i work on pytype [https://github.com/google/pytype], a similar project for python, and it has definitely made business sense. it lets developers code in the language they find most productive (largely due to its dynamic nature), and adds back some of the benefits of static type checking. in particular, it has caught a lot of bugs that would otherwise only have shown up in production, and perhaps not until some rare code path was hit.
It's not like changing to typed Ruby wouldn't affect the code bases. They'll end up having something that will resemble Ruby, but likely won't be quite Ruby. It's unlikely they could automate it. They'll have to rewrite a lot of code and typically, when you do that you also want to refactor obvious problems, so you end up rewriting big parts. And that's in addition to the cost of trying to make Ruby typed.
Or you could leave the code base as it is and extract functionality out and rewrite it in something more manageable.