Sorry man, but Journey to the ... is bonus no. 2 so it can't be also bonus no. 3. :D
No need to be sry!;) But I said an adventure like(!) ..., I meant I dont expect an game newer than 2008...
Did you see my post in the Groupees thread? Jack the Ripper is extremely likely to be the last bonus:
"So.. I think we can count on Jack the Ripper being one of the bonus games. Shifty said there are more "keys" to come, and the current bonus is DRM-free. There's only 1 more frogwares title left on GOG.. so the 1st or 2nd key has to be Jack the Ripper. My guess is they're saving that one as the last bonus. "
Journey to the Center of the Earth was the first key, Jack the Ripper will probably be the second unless Shifty slipped up with his wording. I'd say it's 99% likely to be the game.