I went ahead and read the (reputable or not) spoilers via the ML .. up to a point because I wanted at least some of the movie to be a surprise, if any of the spoilers turned out to be true. And upon reading them, grew to be ... concerned, in the manner which you seem to be concerned, and on the same matter.

I'd become quite fond of Elizabeth, much to my surprise. But I think this Will/Jack/Liz threesome (and not a threesome in that sense, which I might actually enjoy) would just push her over into Suedom. I really think it would. She had two men vying for her attention in POTCI--she damn well doesn't need three.