XBAP? Betcha can’t remember what it stands for, let alone use it. The reply to the first point is XML Browser Application, and to the second part frankly not many people do use it.
There are several reasons for the lack of love I suppose. Since it’s a special kind of browser app, it needs to operate in Medium Trust to be the most effective, and yet even IE9 balks at running them (you have to confirm that you really, really want to run this particular app, which kind of defeats the object). The Medium Trust limitation (along with other security limitations) means that we spend an inordinate amount of time trying to get round these narrow-scenario restrictions instead of providing broader-scenario features. Even with these workarounds, some of our controls still don’t work in an XBAP environment.
It is equally galling when there are two very well supported channels for creating rich internet applications: ClickOnce and Silverlight. We use ClickOnce ourselves for our internal applications, and it works very well indeed in that environment. And, despite all the doom and gloom and unfounded rumors about where Silverlight is going, it is still the premier method for creating rich-internet applications.
All this is leading to the fact that we have officially retired our XBAP support in 11.2. We recommend using ClickOnce for your WPF applications, or transferring over to Silverlight. Remember with DXv2 we have control parity between WPF and Silverlight.