You are right that transparent high-bandwidth satellite fall back is not in the cards at the moment. I will challenge you that high bandwidth is a hard requirement in this case. If Apple can integrate emergency short text + location capability at a low marginal cost, it will make iPhone platform more attractive to people who aspire spending time outside of cell coverage.
First, let's examine some limitations we are dealing with:
1. On the receiving side the trade is power projected on the receiving terminal vs bandwidth. At lower bandwidth we can have quite reasonable power requirements, think GPS antennas. High bandwidth applications are all limited by FCC power per cm2 projection limits. Without those limits LEO satellites could focus transmit onto a much smaller area and enable high-bandwidth receivers that are basically cell-phone sized. Given that GPS is a thing, we can definitely have low-bandwidth phone integrated satellite antenna.
2. On the transmit side primary trade is again transmit power vs bandwidth. Iridium phones are a thing https://www.iridium.com/products/iridium-extreme/, so low bandwith transmit is feasible.
Overall, I think it is quite unlikely that Apple is adding a dedicated on-handset satellite coms. It is possible, maybe even likely, they will be enhancing existing satellite communication capability or adding external devices. Even if they are enhancing satellite coms the provider is definitely not Starlink because phased array power requirements are staggering for mobile applications. So, assuming there is some truth to this leak, it is maybe 1, probably not 3, and almost definitely not 2:
1. Upgrading the existing GPS capability with new antenna / silicon. Most likely to support other positioning constellations https://www.quora.com/What-are-the-competitors-to-GPS, but in era of SDRs maybe sat signals in general.
2. The claim specifically talks about phone/text calls, to make that happen they will either need to integrate with Iridium or back a new not yet deployed service. On Iridium front there are a couple of problems, but they don't seem insurmountable: Iridium modems are expensive and iPhone power/thermal requirements will mean developing logic that is significantly better than anything on the market. Of course Iridium IP licensing or company acquisition would be big news breaking quite a bit before we see any devices, so this is almost certainly not happening.
3. First party integration of external satellite antenna into iPhone ecosystem. Introducing Apple emergency beacon. Deploy this beacon anywhere in the world and get emergency communications for affordable* price. Basically a modern, Apple sleek, version of https://www.iridium.com/blog/2012/05/23/iridium-connected-de... .