However, WM_CLASS comes to rescue. Android Studio's WM_CLASS is set to "jetbrains-studio" and we can match that. (This was gathered using xprop.)
Just add the following lines to the end of i3 config file at ~/.i3/config
assign [class="jetbrains-studio"] 2
This makes Android Studio launch by default on Workspace "2".
Tested for : Android Studio 1.2