I want to use the condition "channel changed to" in triggers

I want to create a trigger that fires actions based on switching the channel. In most cases that applies to talk tickets and messaging tickets in which we often change to E-Mail. 

In my specific case I would like the subject to be changed as soon as the agent switches from Talk/Messaging to E-mail because I want to avoid the agents using the standard “Call with Caller” “Conversation with xy”. I now realize this might be another feature request because one can't choose an action that changes the subject 😅 Anyways I'm sure there's more cases for this request.