Adding myself to the list of people who has successfully managed to get hotplug *partially* working with the Alpine Ridge 2.0 card. I used Method #1, on a Gigabyte Z370 AORUS Gaming 7 board. I had to modify the SSDT to account for this boards ACPI path of RP21.
Huge huge huge thanks to everyone who's gotten this as far as it has. It's come an incredible way in such a short while.
I'm still waiting on my thunderbolt audio interface to get here, so my testing is somewhat limited right now to utilizing Thunderbolt 3 as a USB C 3.1 connection, but something interesting I've discovered in regard to the thunderbolt cable that connects the card to the motherboard, is that the cable, at least for me, seems to be the piece that allows USB to function across Thunderbolt.
When I remove the cable, no matter what I do under OSX, the device will not become active. I've tried all 3 methods, as well as several other SSDT and Arbitrary Injection without the cable. I expect once I actually get my legitimate Thunderbolt audio interface in and retest everything, I'm probably going to find that it will function without that cable being connected, but time will tell.
In the interim, utilizing Method 1 with the cable connected allows me to boot with my current USB C 3.1 (connected straight to Thunderbolt 3 on the card) completely turned off, and the device syncs and works under OSX just as you'd expect. I can turn the interface on and off, reboot and shut down the computer, and it comes back up each and every time which is fantastic!
The last remaining piece of the puzzle for an otherwise perfect implementation is, just as others have experienced, sleep breaks thunderbolt functionality completely until I reboot OSX. So very close. Hopefully we can continue to make some progress at this and get over this final hurdle.