New-Message and Thread views currently lives in the same object ThreadUI. They share some concerns (sending a message, the composer, possibly showing the thread), but they also have differences (behavior when sending, recipients panel, header, subheader, composer height, draft saving and recalling behaviors, thread content). Also, having them in the same object makes it more error-prone when transitioning from the new message panel to the thread panel. As a result, it makes sense to separate them. It will also make sense to move the common components to external objects as well.