What conditions? You asked how a nVidia user could use A-Sync and I gave you a possible response.
I've also told you that per your definition A-Sync is NOT vendor locked as it's not proprietary.
You are the one not understanding that A-Sync is not FreeSync.
We don't know if A-Sync will work on nVidia or not, we just know that they do not officially support it. Don't confuse both!
Well, the definition stated it that being proprietary was the most common reason, but not the only reason. So no, that is not true.
It simply states that if a customer cannot easily transition to another vendor, that customer is vendor locked.
We are talking about the possibility that might happen. Not what will happen. It is one situation, and under that condition, the person is locked-in to a single vendor.
That hypothetical situation is that a person buys an A-sync monitor for variable refresh rate on his Windows gaming PC. Nvidia and Intel do not support A-sync (remember, hypothetical situation), and only AMD does.
That person is vendor locked-in to AMD because he cannot easily transition to any other GPU vendor and get his A-sync monitor to have variable refresh rates.
Unless something changes, such as software being available to make Nvidia and Intel hardware work with A-sync, that person is locked-in to AMD. It does not matter if the VESA standard is open if the person cannot use it on anything but one vendor.
That is my last response to you on this. If this does not make sense to you, you clearly are just disagreeing for the sake of disagreeing.