I bought an AVT-852 last year, and it registers in DHP just fine (as it does when you run DHP for the first time after an install), BUT I told him specifically I would be using it with DHP software, so if there is some workaround that is required, I have it. The only way we'll know for sure is if someone buys an AVT box now.
I have no idea what that registration process does. I'm just really puzzled about this whole thing. I even posted on the DHP/HPTuners Facebook group and got help from Charles directly when I was having issues getting the software to run. I even sent him over a BIN file for my Regal that was, for some reason, unsupported in DHP. I guess all good things come to an end. I suppose I should be glad there was even an alternative in the first place from the clunky Keyspan adapters and paying $Texas for HPT.
Edit: I also don't know if we should really post that direct communication you had with him. Mike is a really stand-up guy, and I asked him a few questions about how the AVT hardware interfaces with the car, and he was more than happy to write me back with tons of documentation and information. I'd hate to get him in trouble with someone or cause a "bridge to be burned" if Charles ever decides to sell DHP again.