There are 2 glaring weaknesses in Trillian for iOS. One is the ability to respond to messages from the lockscreen/ControlCenter. And yes it is a possible feature to add in iOS 9. IMVU is a chat app that has that feature built in.
Second issue is there is no background app refresh option. Meaning after 15 minutes of inactivity the app stops running in the background which is absurd. Trillian should receive messages as long as youre signed in. Not sure why the developers are so determined not to add that feature.
xMattPerkins about Trillian, v3.1