Isn't every new mobile standard effectively a complete redesign of the core network anyway?
Sure, it'll take decades to be fully rolled out, but that's true for every large-scale change. The real problem is that it's not in the interest of stakeholders to have end-to-end security.
Judging by this and your other comment, you seem to have made up your mind that the powers that be are not interested in end to end security. You seem to be ignoring (or disregarding without explanation) similar engineering feedback independently provided to you by different people. Good luck to you, sir!
Confidentiality in networking is entirely possible and rolling out such a system would make carriers instantly liable for every phone and internet connection they fail to wiretap.
5G has redesigned several core identifiers to make it harder for middleboxes to MitM/intercept traffic for a specific target. This has led to slowdowns in 5G rollout all over the world, as carriers needed their suppliers to figure out how to wire tap their customers now that they couldn't uniquely identify a customer by a static identifier anymore.
Carriers may have the best intentions for the security and reliability of their customers, but they're legally obligated to deliver plaintext dumps of phone calls on their network somehow. Same goes for other unencrypted side channels such as SMS.
If 6G redesigns the entire network to be fully E2EE, it's essentially illegal to roll out as a carrier. This isn't an engineering problem as much as it is a legal problem.
There are also financial challenges in a secure system. You need to know who to bill for long international three-way calls. That sounds easy, but because of backwards compatibility and many different ways to do roaming, doing billing for mobile phones is an entire industry in itself.
By stakeholders I don't mean the telecom industry, but the governments regulating it. Lawful interception is non-negotiable, and (working) end-to-end encryption would break that, so I predict that we'll never see it on the POTS, VoIP or circuit switched. (And even OTT VoIP is under constant political attack.)
> You seem to be ignoring (or disregarding without explanation) similar engineering feedback
You mean the other "Bellhead" comments explaining why it's technically impossible to do something on the POTS that's been solved in OTT VoIP for years, like real-time end-to-end encryption using block ciphers etc.?
Yeah, I do discount confident statements declaring something technically impossible when I've been happily using such a system for the better part of a decade.
Sure, it'll take decades to be fully rolled out, but that's true for every large-scale change. The real problem is that it's not in the interest of stakeholders to have end-to-end security.