Most likely this is why the CPUs are all limited to 16GB. It's likely when they unwrap the 16 inch MacBook Pro, it will open up more configurations (more RAM in particular!) for the 13" MacBook Pro and hopefully the mini.
Going into the event, my thinking was that they'd have two aims:
1. "Wow" the audience given the anticipation without a full overhaul of the range.
2. Deliver some solid products that enable the transition while being effective for non-enthusiasts.
From my viewing they hit both. I expect they'll fill in the range next fall with bigger upgrades to the form factor.
I agree, It almost feels like they are going to have 3 main M Series CPUs. This one. One for the iMac and higher end MBPs. And perhaps a third for the high end iMac/ Mac Pro.
It's even easier to explain than that. The RAM is integrated into the CPU. While there are a few SKUs here, Apple only designed and built one CPU with 16GB RAM. The CPUs are binned. The CPUs where all RAM passed testing are sold as 16GB, the 8GB SKUs had a failure on one bank of RAM.
There are no 32 or 64 GB models because Apple isn't making a CPU with 32 or 64GB of RAM yet.
Most likely this is why the CPUs are all limited to 16GB. It's likely when they unwrap the 16 inch MacBook Pro, it will open up more configurations (more RAM in particular!) for the 13" MacBook Pro and hopefully the mini.