I think it’s too late for Apple to do this now. The genie is out of the bottle, and there’s too much competition. It might have worked back when the iPhone was far ahead of everything else, as single carrier did, but it won’t fly now. Even Apple realise that, hence the availability of fully unlocked iPhones these days. If they go back to locked down carriers now then people will just switch to Android or Windows or whatever. Even US customers, who were used to lockdown and extortionate charges, have seen that there is an better alternative.
The only way this could work would be if there was agreement between all manufacturers, as well as the carriers, and I can’t see that happening. There would be too much protest, and it would inevitably lead to serious antitrust and monopoly investigations which none of those companies want.
I hope I’m right anyway. I know I wouldn’t be paying £10/month for 240 mins voice + unlimited texts and data on my iPhone4s if Apple had anything to do with it.