Ranked play on arena will not happen, don't get your hopes up. It just isn't the focus of the game.
Same goes for the levelling up of the character and match making.
If Arena ever gets developed we will get something much simpler, like pick character level, get X attribute points, Y skill points and choose from a list of items and skills.
I highly doubt it will go too much further from that. Mods could improve a little bit more on it, but not create systems for ranked play and account levelling up.
Furthermore, consider that this is mainly a Single Player or Coop Multiplayer game, preventing players from cheating is not currently something they have to enforce so...