Will there be an OS X version ?

I'm sorry, but the answer is no...
It's not that I don't want, but right now it's simply impossible.

Can Wapp pro list all the windows of all the applications in the main menu instead of in submenus ?

Sorry, right now there's no option for that, and honestly it's not simple to implement, so I can't guarantee it will ever be available.

What happened to the support of the Application Switcher palette in version 3 ?

This support has always been tricky, and I've never achieved the level of integration I wanted. So I just pulled out this feature.
At first I wanted to make it available as a separate module for Wapp pro, but it's not so simple to do. So instead, from version 3.1, I've included my own application switcher in the menu bar. I hope you'll find it convenient....