Super Kiwi 64 aims to be that, from what I can see.
I also have such a game in my to-do list, but because that to-do list has like 50 items, it may take 10 years to actually happen.
Viewing post in Open 64 Bits? More of a question or questions.
I saw and played that one; though I somewhat disagree to an extent. Once you beat the game, it becomes the player's playground and they put in some extras such as a cut level or 2; though it doesn't accomplish the idea of an open world game like Morrowind or Skyrim as the game funnels you to a single goal like Banjo Kazooie as your given levels where you need to overcome with your skills in platforming and problem solving.
Still; it's a good call out. :D