In theory, nothing prevents a Windows 8 app from communicating with a desktop application or with the underlying Windows environment. One tool conspicuously missing, for example, is a Windows 8 app that handles file management chores. I'm hoping Microsoft will be encouraging more integration between the two parallel universes the company has built into Windows 8.
Cross platform development issues and techniques
Microsoft is trying to bootstrap itself into multiple operating environments. It's attempted this in the past, with little success. But given the increasing mobile nature of modern computing, the company can't rely on desktop Windows and desktop Office to remain competitive.
Microsoft's developers have seen some success in the past with cross platform development between the Xbox 360 and Windows PCs, in the form of PC games. As the distinction in users' minds between tablets, smart phones and PCs becoming increasingly blurry, applications that can run cross-platform will be critical to Microsoft's success. One measure of potential success will be how enthusiastically Microsoft's cadre of developers embrace the cross-platform message.
PC gaming and touch
I'm sure we'll see plenty of lightweight, Windows 8 game apps that use touch. I'm more interested in how larger, desktop enabled game titles might embrace touch. Eugen Systems created R.U.S.E.several years ago. R.U.S.E. is a real-time strategy game that enabled multi-touch in a Windows 7 enviromment. Firaxis is readying an update to Civilization V that will enable multi-touch support in the game. Hidden Path Entertainment will be adding touch to its popular Defense Grid: The Awakening tower defense game. But other game developers have been pretty quiet about Windows 8 and touch. I'd love to see how game developers might integrate touch and gestures into the PC games, particularly role-playing or action titles.
Final thoughts: applications beget users
At some level, this year's Build conference will be anticlimactic, since the event is going on after the Windows 8 launch. In some ways, though, that make Build even more important. Windows 8 is more of a known quantity among developers now.