According to , Arc System Works will be showing off the title at the upcoming Tokyo Game Show. The title would seem to suggest that it's a remake of the original Renegade, but that's certainly not a given. It could be a complete reboot of the series.
Kunio games have appeared on the Nintendo DS, but Millions has been mainly focusing on light sports titles such as River City Sports Challenge. The new 3DS game could be another sports title; or who knows, it could be a fighting game.
Until we find out, the best take on River City Ransom is still Scott Pilgrim.