This whole discussion is a bit hypothetical for me, since I have no idea what the dilemma under discussion does. I am not realistically able to play tournaments so I will likely not see this card for quite some time. But nevertheless:
1. In a tournament it is critical that I can verify that a card is legal. I like Allen's solution -- spoil the relevant gametext but keep the image hidden or heavily obscured to preserve the coolness/surprise factor when you see it. Maybe hide it somewhere obscure on the CC site. But there needs to be some way to distinguish "this is a legit preview card" from "a photoshopped dream card printed out with a white border that I claim is a new preview".
2. If there is a "surprise" card, it should be "I get to do something cool, and my opponent is excited to see a cool new card too" rather than "I get to screw over my opponent who wasn't expecting it because they're not part of the in-crowd". The first Decipher preview was the USS Defiant in DS9, which fit this role perfectly. It's a cool card, it let Decipher focus the set on the first two seasons while addressing the inevitable "how can you have DS9 without the Defiant" questions, AND was powerful enough to be useful, but not gamebreaking if it showed up on the other side of the table. A powerful dilemma "surprise" is much sneakier and feels like a sucker punch. (*)
Centurion Kirk is an example of a preview that avoids both these problems: it shows up on the website, and it's a cool/flashy card that doesn't feel like a cheat if your opponent plays it. I'd be legit excited if I saw my opponent play something like Centurion Kirk even if I didn't know the card existed
. A surprise dilemma that devastates my crew, not so much.
I understand the argument about equal accessibility to players, but I also acknowledge the power of having an incentive for tournament play and CC revenue. So on balance I'm fine with quasi-secret previews as long as they address the two issues above.