I dont think you could make Berserk into a fully fledged RPG.
What I'd like to see, is a Berserk Action/Adventure game with RPG element.
For example, you start off as young Gattsu, the first few levels or area's consist of training and teaching from Gambino about how to preform basic moves etc, and get familar with the game's controls and gameplay.
The you can live the semi-mercinary lifestyle with Gambino's band of mercinaries, but with Gambino initially watching your back in what would have to be real time, action battle scene, with a number of both ally and enemy AI controlled troops.
Then as you get stronger/more skilled (rpg style) the story line progresses to where Gambino is injured. Then the murder of Gambino by Gattsu can be the boss for the first stage of the game, and Gattsu's escape from the other mercinaries the transition to the next stage of the game.
The next stage could be Gattsu roaming around the country side looking for 'work' as a mercinary, with varying/random missions/task, which could be undertaken from either as part of an army in a battle - harder now without help from Gambino etc - or as an individual, eg basic/simple assassination.
Then, once again but character advancement, you come to a boss - Pazu-So, followed by the fight caused by Corkus's robbery attempt, and the self ransom with Griffith which eventually leads you to the join the hawks.
I'm probably rambling now... just repeasting the story line you all know so well / better than me.
But just imagine, the Hawks versus Immortal Knight battle, mapped out as a multiplayer map, players being able to join either side as either main characters (Gattsu, Caska, Adon etc.) or just members of either band, complete with multiple AI bots, in a real time battle.
Or have I gone astray?