Okay, so macOS 12 Monterey, to be released in September 2021, will no longer support the Late 2013 MacBook Pro that I own, and the new machines available no longer have USB-A ports.
Will I be able to use a USB-4/Thunderbolt hub with USB-A ports and still update my Diamond saber?
The answer is yes; yes, it works fine, as verified with an M1 MacBook Air running MacOS Monterey 12.0.1 this evening. It also works just fine when an Obsidian v4 saber is plugged in instead of a Diamond saber; it detects and identifies the boards properly.
As usual, the trick is using a cable (mini-USB for the Obsidian v4, and micro-USB for the Diamond) that will transmit both power AND data.