Yes, I think it is possible and just the sort of thing they would do, certainly I do remember opinion being divided with Jack at the wedding, some saw it as paternal, and clearly some saw it as attraction. I think that is partly the show being a tease, allowing for fan wank and people to hang onto their interpretations, but on the other hand they have had Jack reject Gwen right from the start, and put her with Owen in the first season, when there was no need if they had wanted to develop anything with J/G. That was scuppered with the Owen affair really, unless you killed Rhys and even then allowed some time, it just would never work. (Not to mention that I don't see it working anyhow, no chemistry)

I really think your theory would be fun, the scenes would need to be a flashback though.