How can I make Siri use non apple apps? Is there a general way extend Siri on iOS 8 to use other apps?

For instance, I am not using the apple E-Mail app but "myMail". I'd like to make Siri use this app when telling her to write an e-mail? 

By extension, can non-apple apps for sending instant messages, listening to music be plugged into Siri?
This is currently not possible. Siri is only able to use Apple's standard apps, sadly.