I don't think any ways of doing this can be 100% fair. People will complain no matter what happens, but CDPR are good to adapt just like they did when they saw people were not respecting the NDA for KTS.
I don't think there should be any privileges, at least not much and/or not for now. It's true that 100% random means a lot of people will play and never give any feedback, will just not play or not really understand the game (a lot of people follow the gwent page and seem to have no clue what the game is). BTons of potential good testers are ready to jump into action and it would not be fair to them if it wasn't random. It's not because some people are already on the forums that 100000 others won't join if they get a code. It's like Blizzard that gives beta codes to streamers beforer players and some streamers really do not deserve codes more than other people. It's supposed to build up hype, but IMO it builds up frustration. I really don't want to know that Gwent is live but only a small portion of people are playing and by "pure coincidence" it's only known people.
It's true that I posted some feedback for KTS and even got a red reply, but other than that I keep away from these forums because I can't handle the hype. I don't think I deserve a code more or less than any of you that posts more or less than me. I want to get a code really really bad, but I also want my friends who barely know the game to get in and test it fully, because I know they will.
Please remember than in the end, CDPR will always send more invites until they get the wanted results. So if people are not playing or not giving feedback, they will send more codes and adapt. Maybe after first wave they will notice us on the forums and give us keys, who knows, but when it starts I think they have to be fair with everybody