Server side makes more sense. WPF is an UI framework, even it includes WPF, the user experience will be bad just because it looks so differently than native apps.
OTOH, WPF apps already look different than native apps on Windows. Look at pushbuttons for example, they are completely flat in WPF and have a gradient in Win32. (WPF controls are not drawn via uxtheme, but have styles defined in XAML.)
WPF is part of a trend I believe to see, going away from strictly consistent UI styles:
QT used to emphasize simple widgets that you could theme consistently. With QT quick the emphasis is on individual per-app styles themed with css (but you also have the old widgets). Very similar situation in GTK3, where cross-desktop themeing is deemphasized (they removed support for changing theme colors, hid the theme changer in gnome-tweak-tools, and some developers advocated removing themeing altogether). At the same time, individual GNOME3 apps experiment much more with nonstandard widgets and CSS than before.
Windows 8 "Metro" apps are similar. With the simple, clean design language, I thought they would be really design-by-intent. A la "I want a list here, and I want to link it to a detail view. My elements have these properties. Build me a CRUD interface and spice it up with these colors." and it would generate a Metro UI. But instead, after playing with Visual Studio, I find it's almost the opposite: "Place a rectangle at these coordinates, a label there. When the user clicks here, run that code." There is very little in the development experience to encourage consistent UIs, and you have to look up stuff like recommended font sizes manually on MSDN. Naturally, it makes it impossible to upgrade the UI style over all apps in a later Windows version.
Same in Android. Try to make an app look up-to-date, even on currently unreleased OS versions is impossible. UI code is way to low-level, considering a huge fraction of apps are just fancy list-views.
I could go on for a while. The point is that (unfortunately) UI consistency is not a priority nowadays (maybe except on OSX), at least when it comes to tooling (the efforts of many developers to still make consistent UX/UI are very laudable). And compared with the competitors, you could write at least as nice apps in WPF.
WPF is part of a trend I believe to see, going away from strictly consistent UI styles:
QT used to emphasize simple widgets that you could theme consistently. With QT quick the emphasis is on individual per-app styles themed with css (but you also have the old widgets). Very similar situation in GTK3, where cross-desktop themeing is deemphasized (they removed support for changing theme colors, hid the theme changer in gnome-tweak-tools, and some developers advocated removing themeing altogether). At the same time, individual GNOME3 apps experiment much more with nonstandard widgets and CSS than before.
Windows 8 "Metro" apps are similar. With the simple, clean design language, I thought they would be really design-by-intent. A la "I want a list here, and I want to link it to a detail view. My elements have these properties. Build me a CRUD interface and spice it up with these colors." and it would generate a Metro UI. But instead, after playing with Visual Studio, I find it's almost the opposite: "Place a rectangle at these coordinates, a label there. When the user clicks here, run that code." There is very little in the development experience to encourage consistent UIs, and you have to look up stuff like recommended font sizes manually on MSDN. Naturally, it makes it impossible to upgrade the UI style over all apps in a later Windows version.
Same in Android. Try to make an app look up-to-date, even on currently unreleased OS versions is impossible. UI code is way to low-level, considering a huge fraction of apps are just fancy list-views.
I could go on for a while. The point is that (unfortunately) UI consistency is not a priority nowadays (maybe except on OSX), at least when it comes to tooling (the efforts of many developers to still make consistent UX/UI are very laudable). And compared with the competitors, you could write at least as nice apps in WPF.