The worlds collective programming experience doesn't really back that up. Almost every language drops (or makes optional) type support when constructs become too complicated, or they become so complicated no one can understand them.
Languages with the best type systems (OCaml) aren't particularly popular, while languages we think of as strongly typed (eg Java) have big backdoors to allow people to bypass the type system.
On the other side, weakly typed languages are adding typing-like features by integrating unit test facilities into the environment (which - optionally - catch many of the bugs typing can help with).
Like so many things, optional typing might seem impure, but often messy systems are the most robust.
Summary
Gilad Bracha discusses Dart, its type system, interfaces, generics, ADTs without types, built-in factory support.
Yes, but it's not the same as outdated comments. A well featured optional type system will let you know that is happening. An out of date comment will just continue to deceive.
Or they going to do what they do with compiler warnings and turn them off as soon as they see one?
My advice, is not to work in such shops.
I guess... my gut tells me that you should either have types, or not have types. Being in the middle creates too many opportunities for cognitive dissonance
As if there's a lack of them on the ends of the spectrum compared to the middle. We will find out if it will be more of a mess, so many will have gut-calibration data.
Are people really going to run in checked mode to verify their code? Or they going to do what they do with compiler warnings and turn them off as soon as they see one? I'm sure there will be a million blog posts titled "Dart Best Practices" that will say "do not use checked mode, it slows down execution and prints confusing messages". Of course, any bugs in checked mode will mean people will need to get their production systems working by ignoring checked mode.
I guess... my gut tells me that you should either have types, or not have types. Being in the middle creates too many opportunities for cognitive dissonance, too many opportunities for sneaky bugs, and too many opportunities to keep having this debate. It's one of those things that seems really smart and cool that, on a practical level, will probably turn out to be a complete waste of time and a total distraction.