On: A new approach to local multiplayer / splitscreen ...

[chckens]

2008? Pah! How about 1991’s Toejam & Earl on the Sega Genesis ?

https://youtu.be/SPQXmZR7JWo?feature=shared (From about 2:30)

Now get off my lawn.

[cubefox → chckens]

Though this always created/merged a horizontal split once characters were separated/close enough, while the modern games rotate the angle of the split based on the relative positions of the characters to each other.

[pimlottc → chckens]

Direct link to 2:27 [0]

0: https://www.youtube.com/watch?v=SPQXmZR7JWo&t=147s