The market is as bimodal as ever on the device side: On one side, you have small, battery-powered, (mostly) omnidirectional device antenna, portable devices that mainly operate in the L-band, which works much better in these conditions; on the other side, you have highly sophisticated, steered, high power (dozens of watts) antenna arrays operating in the Ku or Ka band.
On the satellite side, both can be served by the same satellites, as has been the case for e.g. Inmarsat's I-6 series and Starlink's direct-to-cell capable satellites (I believe these all include Ku-band coverage as well).
The SNR in Shannon’s Law has a log in front of it, but spectrum reuse is more or less linear. If there are five visible satellites and I can null out four of them, then I can receive from and transmit to the fifth without substantial interference. (I’m not saying this is easy! Contemplate how many WiFi generations have had MIMO and how limited it still is.)
So I believe that it’s comparatively straightforward to demonstrate a shiny new direct-to-cell system with a single phone on a stage, but achieving usefully large aggregate bandwidth in a dense area will be more challenging.
FWIW the problem with Iridium, historically anyway, was that available bandwidth was very low, so they had to charge a silly amount for usage of that bandwidth, so very few people used it. Iridium used low-ish frequencies, with narrow bandwidth, and (I think) no MIMO whatsoever, not even polarization diversity.