I thought the very same thing that the next Character will be a young boy. Maybe around Kooh's age. There are currently 4 male and 5 females for a total of 9 Characters. To match up the gender ratio, it would make sense to add in a guy. The next question would be the age group. Judging how popularity would go, either a young or a teenage guy would be best suited. Bob has already fulfilled the role of the old man part.
I've been eying on this one Character for a long time that has been popping up in their artworks lately. I first discovered this unknown Character when I saw him on a Pangya site long ago. Then later, I find more artwork pictures of him in Super Swing Golf, and now Pangya Portable too.
Even though he could have appeared in Season 4, I assume they released Lucia instead for popularity purposes. I'd say it's a good move for them because before Lucia appeared there was a 4:4 gender ratio anyways. So their decision to release either a male or female Character is pretty much one sided.
But like I said before, this is only a prediction coming from me. Who knows, they could release another female Character for the sole purpose of adding more money in their pockets. But if most of you really think the next Character will be a male, then I think Ntreev will respond to that same concept too. But first, lets give them time for more important things since they are in the works of making Season 5 at the moment. ;)