Btw. I don't care about the language, but I care about support of IDE's and Tooling and I hope that you built around the Dart Tooling of IntelliJ, then I would give it a try!
Dart's IntelliJ tooling is built on top of a reusable analysis library written in Dart. It exposes a service-like API so that it can be integrated into lots of different editors/IDEs without each having to reinvent the world.
Just to be clear, this is full-featured, rich static analysis, not just parsing and syntax highlighting. The entire static type system of the lanugage, including the new stronger type checking is in there.
The Atom plug-in uses that too.
Given that WP10 and Windows 10 should have a similar "universal" runtime, maybe once you are done with your android/iOS to WP10 port it will work quite nicely on Windows 10 after you update the UI to support larger screens.
So, hopefully once enough people are on Windows 10, the windows (phone) 10 ecosystem will be attractive enough that people want to build things for windows 10, rather than the web.
I have no idea if this strategy will work out, but it's what I sort of expected windows 8 to be, but hey, maybe the ship hasn't sailed so far as to make this pointless.
I used to work at MSFT though, so this please excuse the bleakness shrouded in the unwarranted optimism.