The "+" opens the keyboard and then becomes an "x" which must be pressed again to revert back to a "+" to add attachments. If I'm typing already, this isn't an issue as I only need to press a single button. It is however annoying if I've read the text in a preview window, especially on nougat and I just want to send a quick picture, gif(which I love), or emoji. Maybe a swipe up to open the keyboard and keep the "+" for attachments...