This would make some people skittish, but once the show is over, I personally would have ZERO issue with a Lost attraction. My idea would be 2 attractions in one. The pre-show would be an attraction in and of itself, a 360-degree simulation of a cruise where you meet one of the characters from Lost who isn't dead by the time the show ends. Probably Hurley, laughing about how he'd never be caught dead flying again, haha. Only one by one, many other characters from the series walk by, all doing that "What are you...and you...but if you're all here...and I'm here...oh crap..." Hurley tells you to stay close if anything gets screwy, they've done this before. Suddenly a rumble, a pop, and the cruise ship is magically grounded on The Island. After some fun with the smoke monster and some of The Others chasing you, you exit the "ship" and board a Dharma bus to get to the shore, where there's a chance...JUST a chance you can get back to where you're supposed to be.
Now if they REALLY wanted to achieve some sense of "reality" for the ride based on the reality of the series, and as long as dreaming is legal, the first part of the attraction would release people in a tunnel where omnimovers would take you to the second part of the ride. That tunnel would go UNDER the Seven Seas Lagoon and drop you off on Discovery Island, which would be converted into the latter part of the attraction. And when the ride is over, you've been "dropped off" in the middle of WDW. Once you're done with the attraction, you can either take an omnimover back, or there are boat shuttles that take you to a special re-entrance just for Lost riders, or a boat shuttle that will take you to the TTC, if that was your last experience of the day and of course, the boats only take people FROM the island, not TO the island). Because the attraction's timeline occurs AFTER the events of the series, there's no need to worry about continuity, in fact, you have characters essentially saying "oh, no, not again," which allows the Imagineers to take you through iconic moments from the series OR create a whole new adventure, perhaps one that the characters hadn't yet experienced.
That's my Blue Sky synopsis and I'm sticking to it.