Game companies love keeping secrets. They don't want anyone to know anything about what their doing, until the last possible minute. There's a few reasons for this, the primary one is what they call "building anticipation". They want customers to be in a frothing frenzy to find out what the new thing is so they'll run out and buy it as soon as it becomes available.
Wait...that doesn't make any sense. How does just finding out about something translate into wanting it extra bad, extra now? Maybe this culture of secrecy has been a big mistake. Maybe the answer is to keep your customers in the loop about exactly what's coming the moment you can reasonably tell them. Maybe that notion can be taken even farther...
What if the entire R&D process for a game expansion were public. Throw out the usual bunch of playtesters (great as they may be!), throw out the non-disclosure agreements, and throw out the notion that if the public doesn't know what's coming, they'll be more apt to buy it.
Invite your customers to participate in the R&D process. If you game company owns its own intellectual property and its own game mechanics, it's not like your competition is going to be able to steal any of the ideas. Your fans, on the other hand, will get the chance to put in their opinions. Some of the are experts at your game. Then, and this is the hard part, you have to listen to them.
This does require R&D (the expansion's writers) to accept that the public's ideas are worth paying attention to, and a lets face it, a lot of stuff that you'll see won't be what you're looking for. Wait, here comes an important point: Some of it will be.
Another thing to remember is the expansion will still be in your control. The public doesn't get to make decisions, but they do get to question them. The public can't force you to use their ideas, but they do get to present them. You may be forced to better explain (at least to yourself) why you've made one decision or another. That's not a bad thing. It will be more work. Maybe a lot more.
So you've done it. You've posted weekly updates with new rules and PDF files so playtesters (that is, absolutely every fan of your product that wants to be a playtester, not just a few that you 'trust') can fabricate their own cards/playing pieces/whatever. You've read the comments based on those weekly reports and maybe even made some adjustments based on those comments. You've finished. In a couple of months, the expansion will be released.
Will a product like this, where the fans have literally been able to contribute to its content in a real way, have a better or worse chance at success than a product they've never seen before, because it's been a closely guarded secret?
I think I know the answer.