DPC started that rumor himself talking about the fact that Season 4 will feel very different like the 3 Seasons before... some are assuming that the whole season 4 might be some kind of epilogue.Well yeah that's a given. Neither Sarah or Mel have the power or the story capability to end a MG relationship. So far only Zoey has had that power and there's a good chance Bianca and Jade have this power too.
With that I'd put Cathy and Bianca very high up the getting some sort of meaningful conclusion list.
If that is the case, there is enough time and content to add pretty much for every girl a meaningful ending with a relationship, i wouldnt count it out anymore after seeing how many sidegirl relationships are becoming more and more important and serious.