With all of the emojis now, having a ability to search for an emoji would be really useful.

Also the ability to save certain contacts to a group so we can change the notifications for all of them at once without having to tediously scroll through all the conversations.

More font color options!
White, black and gray isn't very diverse. I would like to set up certain contact message fonts in correlation to their favorite sports team colors.

The ability to archive and categorize messages by time/contact/subject.

When I reply to an especially long text it would be nice ione able to look at the received message while typing the new one. These are a few examples:

-Scroll through conversion and minimize keyboard.

-Don't automatically reset the message view back to the bottom of the conversation when the keyboard opens.

-Ability to change areas of objects on the screen to maximize view of message or resize the received message view (widen) when replying so more of the message is viewable at once. (maybe fullscreen mode)