Cross Platform Project File Solution
I think this would fir in with the Mobile API, although I could see it as part of the core offering.
Right now there isn't a great way to divide up a project to be able to share code between WP7, Android and iOS.
Many developers, myself included, have been copying project files that end up having the same source files and maintaining a large number of different projects for each platform.
Even if there was a tool that auto-regenerated this project files or something of that nature, it would be better than everyone rolling their own solution to this problem.
If this issue is addressed, and by addressed I mean there is an easy to explain understandable, solid way to do cross platform mobile development with a shareable code base, I think it will go a long way to MonoTouch / Mono for Android adoption.
I'm not looking for an integrated UI solution here, but a way to bridge the common parts so that I don't have project hell.
Stuart Lodge commented
I'm now using Portable Libraries, IoC and Mvvm quite happily.... http://github.com/slodge/mvvmcross
Although the monotouch tooling for Portable Libraries is still a slight pain point.
Jivko Petiov commented
I don't like linking files across projects. This needs to be done with Portable Class Libraries in mind. In the perfect world, a cross-platform solution should have the following structure: one portable core library containing the business logic and data access, and one platform-specific project for each supported platform - Monotouch, Mono for Android, Windows Phone, Native Client, MonoMac, etc.
Paul Du Bois commented
I'm using ProjectLinker to keep my WP7, Monotouch and Mono for Android common classes in sync. Works great. Look for it on NuGet.
Also use the VSMonoTouch VS plugin in order to load and compile MonoTouch projects.
All this stuff has been explained in detail by Jonas Follosoe. Watch his NDC 2011 video for much cool cross platform tips and tricks.