Honestly, I think that Nintendo, should they want to put another Mother character in, would take a sort-of Robin approach to it. Lord Sakurai has said that the reason they chose Robin as a a Fire Emblem rep is that they thought the series needed more reps, but that they didn't want it to be another swordfighter character, since they'd had 3 already. Ness and Lucas are both ranged, aerial characters, and I think if Nintendo were to make my life complete and include another Mother character in the series, it would almost certainly not be Paula/Kumatora, as they could very easily be a Ness/Lucas clone. Our best hope is for someone unique, the semi-swordfighter/semi-magic Poo, the ???/??? Porky, so on. (How would you guys imagine some of these characters playing, by the way? Like Porky for example?)