I always wondered about Jane actually.
I know that nothing was ever concrete but the bit where Hughes said "We've a new maid who has the same story as you funnily enough" or words to that effect, always felt like they were going to go somewhere. But I suppose she was supposed to be the contrast to Ethel, but the thing that's been bothering me - and highlighted by posts on tumblr where Robert fans have been saying that its not fair to judge Robert by our standards because it was somehow alright for men in his position to have affairs - is that Fellows presents the characters, like Ethel, doing "bad" things and then being punished. And that's fair enough if it's by the characters in the show but there always seems to be an air of "this is actually how I think we should approach these things" in his writing.
With that in mind I'm guesses that Ethel's going to swallow acid and be like the dead woman in An Inspector Calls who was so hard done by by the world that she ended it all and then it's everyone else's fault!