The PR here is hiding the larger issue. It's not end-users that carriers need to worry about - as you say, most are on near unlimited texting plans, and it's rather unlikely monthly plans will drop in price.
No, the problem is the general rise of IP/push messaging across all sectors. Carriers do make significant amounts of money from direct connection billing and bulk SMS. As more brands develop mobile presences the need to contact customers through SMS versus alternative methods will decrease. Push messaging is considerably cheaper, and from the end user's perspective often less annoying and more convenient.
Fortunately (for the carriers), most operate globally, and certain developing markets offer vast SMS revenue potential, more than the West ever did. India alone is a massive user of SMS, considerably more so than the US (partly due to the lack of regulation: a lot of those SMS messages being sent in India are spam).