@Tomasz Kubacki: From my expertise with an enterprise level software background: majority of software (including web apps) is developed under Windows, with .NET/Java, Oracle, and deployed on Windows Servers etc. Most projects are done with WPF/C#, some with SL/OOB to simplify deployment and reach on Mac. After professional development with C#, JS web client development (even with a crutch like TypeScript) looks like a we are back in late 90x.
Pure web apps are just fallback solutions or simply are not interesting, because mobile apps are not very interesting for enterprises due to security reasons of mobile devices. Enterprises still don't trust iOS/Android on mobiles. BYOD is a myth in enterprises which care about security.
After Windows 8, most of WPF/SL XAML apps will be downgraded to WinRT/XAML to make tablet-friendly versions.
Maybe FB, Amazon and Co are deployed on linuxes and developing on Macs, I tell what I see - no macs, no linuxes, no Dart is actually seen, thus needed.
What is definitely regretted is that MS tries to abandon such a beautiful technology as Silverlight neither open-sourcing it nor supporting it on WinRT, nor making it cross-platform, embedding in browser like Flash, etc.
Attitude towards Microsoft changing something so drastically and powerful (like for example Web CLR (Silverlight)) always meets strong resistance from masses. However, when Google does the same (Dart is the same Web CLR with fallback to legacy JS VM), people see this like a great innovation.
I don't know how to change this, maybe dropping further development of Silverlight was a big mistake, or XAML as a main presentation layers was too big obstacle for mass adoption and HTML would be better, or not open-sourcing Silverlight CLR was no-go. C# has already dynamic typing, so basically C# is somewhat dynamic language with JS properties in addition to fundamental static typing.
Anyway, I hope Microsoft will make the proper conclusions from this lesson.
The idea of Google is clear, Chrome has built-in support for Dart, so all Dart stuff will be running fast in Chrome on every platform. Other browsers will have to follow to stay competitive by building-in open-sourced implementation of Dart in their engines. Or stay with slow JS, produced by Dart compilers. I see already Google proclaiming "Dart is fastest in Chrome, FF (and maybe Safari)!", developers are moving to Dart, increasing the demand for Dart VM in the world. When Microsoft would finish TypeScript, there will be already the better alternative supported by most browsers. Who would need JS/TS then?
I believe JS is broken enough to retire it completely. I agree with Lars than W3C will not let it develop into usable web application scope language in next 20 years. So someone has to take a lead there. I hope it will be a software company, not an advertisement one.