I'm curious how many runtime errors persist due to the optionality of the type system. Perhaps code standards requiring all "library" code to be typed would be a good balance.
Most enterprise customers I have worked with, favour dynamic languages just for scripting tasks, while using static typed ones for the large scale projects.
By large scale, I mean, projects with at least three development sites, at least 30 developers, all the different set of skills. With lots of attrition.
The only time I saw it working, was in a project done with TCL, which lacks optional types, but everyone on team was a top developer, the team was small, and located on the same open space. So startup world, not enterprise.