I wonder if they’re looking to do a city-level mesh network that only iPhones get to participate in where your phone can simultaneously transmit and receive on LTE (although I don’t know what kind of regulatory things come into play for that idea).
I think the main advantage is power, security (QC’s software stack was a giant mess last I looked), stability (see previous point) and time to market for new standards into as many products (improving battery life, cost and size of wearables using their chip). I’m sure how long it took them to get LTE from QC in a fit and finish that was acceptable wasn’t a lost frustration (since that’s repeated constantly with 3g and 4g previously too).
Also, at Apple’s scale, I’m sure being able to single source a chip that is vertically integrated across billions of phones means the costs of integrating it into other smaller product lines is even more amortized so more things will get the option of a modem.
It also wouldn’t surprise me if at some point Apple became their own ISP and could really start to add non-standard functionality and not be tied to individual ISPs. Their SOS satellite play is part of that I think but I’m not yet sure how terrestrial internet and satellite will interplay - maybe they need to vertically integrate the cellular modem with the satellite piece to get things to work at good enough power? Or maybe they’ll have base stations repeating satellite internet via traditional cellular/Wi-Fi?
Apple could very well bring innovations to cellular modems that make their products behave more seamlessly or are simpler to use. Additionally they may introduce features that aren't currently possible with Qualcomm's designs.