i dont hate the precedent of this. the messages API should have been opened a long time ago to allow devs to make alternate messaging applications that could directly integrate with the system, and should be available now as an option to replace the bland, feature-lacking, stock messages app.
i would not use fb messenger as my go-to, at all. however, those jailbreakers you condescending people around here mock all the time used to have a legendary tweak called biteSMS that had quick reply many years before apple made it a "feature" and it also featured a robust and efficient "quick compose" interface that the user could call up with a variety of different gestures or button choices. it also had a laundry list of awesome features the user could take advantage of, which included stickying favorites as is now available as of a week ago (lmfao) and message scheduling.
it was supported better than many apps i've used and was a staple for just about every person who installed a jailbreak.
apple relinquishing control of the stock choice for message app would be a monumental improvement to iOS. they barely seem to care about the functioning of the messages app, and as someone who has used a feature rich messaging app, people seriously have no idea not only what they're missing out on, but just how pathetically lackluster the current offering is.