Single-player RPG with not just non-linearity, but with true branching storylines, kinda like VNs.
Most non-linear RPGs follow the formula of slightly different events during the course of the story depending on player choices and then comes the choice that affects the ending right before the "final boss" and those endings are usually not that different, most of them end with "final boss" defeated and one in which player joins "team bad guys". You still go from point A to point B. Even Witcher 2, that fancies itself a game with branching story still follows that formula: no matter who you side with, you still have to go to Loc Muinne in chapter 3.
Let's take Skyrim for example. You can be thane of every hold and head of every guild. "Realistically" that can't happen. What if you could choose only one home and one career? What if guild story arcs were more polished with their own twists and turns and friends/love interests and took about 10 hours to complete?
Not talking Skyrim-specific here (just took it as an example, since most people probably played it), but that's the kind of RPG I want to see: a game with a branching storylines that lead to different places, not just to one same final boss. Doesn't even need to be a good vs evil type of thing. Life as swordsman/soldier would be different from life as a mage/scholar - the people in your immidiate circle, the things that you do and want to do would be different. Not just doing an origin story, throwing you in the world, role-playing a couple of converstions and running to defeat the "final boss". Careers of the swordsman and the mage have to be totally different stories and totally different expiriences. TOR mmo attempted to do it, but it is a very bad example since aside from picking your faction and career at char setup, it still followed "from point A to point B" formula, but true branching storyline is impossible with mmos anyway.
I realise a true branching storyline is hard to do outside of VNs, especially if we are talking cinematic quality RPGs here, but I won't lose hope and if sometime there will be a kickstarter for it, I will pledge my every single penny.