Greetings thanks for the great post!
Wanted to loop back with an update that Apple does allow users to purchase Mac Studio (2022) SSD Modules at the following website:
Enter your Mac Studio serial number then select desktop repair and SSD Modules.
Below are the part numbers and prices:
Please note Apple only allows shipping to select countries ATM.
It's nice to know that it's possible but I imagine that most with M1 Studios would rather just upgrade to the M3 when it comes out and order with more storage as the other improvements would make it worthwhile for a lot of customers. I am happy with external SSD performance myself as the cost per TB is so much more attractive than Apple's storage.