The Dark Souls 2 approach was perfection - open first half, linear second half. I think this is the best fit for Souls gameplay because in the beginning, it gives new players multiple options to progress and lets experienced players choose where to go to build their character how they want, then once you're used to the game and have your character built, it's just a gauntlet of finely-tuned challenges until the end. The "open first half" works well with Dark Souls' interconnected zones but it could work well with ER's open world as well.