I managed to download a similar application (which contains the content block extension just like yours) with the following two changes.
First, both Architectures and Virtual Architectures contain only arm64.
Secondly, Info.plist for the extension and the main application contains the following: restriction of this application / extension to 64-bit architectures:
<key>UIRequiredDeviceCapabilities</key> <array> <string>arm64</string> </array>
Content blocker extensions should only be 64-bit. Not sure if a mixed 32/64-bit application may also contain an extension with a 64-bit extension. To be safe, and since blocking content is in any case the main / only functionality of my application, I made only the application and the extension only 64-bit.
Update, March 2016 .. With Xcode 7.2.1, you no longer need to install the architecture as one comment below the notes. You only need to install the necessary device capabilities and valid architectures. (You can see that this is the default value when creating a new Content Blocker extension with standard Xcode templates.)
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